text
stringlengths 226
34.5k
|
|---|
Why does this Python Flask router return a 400 error when pinged by a crossdomain AJAX call?
Question: I have the below Python Flask router:
@app.route('/create', methods=['GET', 'POST'])
@crossdomain(origin='*')
def create():
if request.method == 'POST':
print(request.form)
title = request.form['title']
url = request.form['url']
new_mark = Mark(
title=title,
url=url
)
new_mark.save()
return new_mark
When I do an ajax call (below) it responds with a 400 error.
$.ajax({
type: 'POST',
url: 'http://localhost:5000/create',
data: {
'title': sender.title,
'url': sender.url
},
xhrFields: {
withCredentials: true
},
dataType: 'json'
});
When I try printing out `request` it prints an empty `immutableMultiDict`. Any
idea why it is giving this 400 and why there is no data?
Answer: Your ajax call is sending json-encoded data. I guess you should decode.
import json
data = json.loads(request.data)
print data.get("title")
|
Writing a Python list of lists to a csv file
Question: I have a long list of lists of the following form ---
a = [[1.2,'abc',3],[1.2,'werew',4],........,[1.4,'qew',2]]
i.e. the values in the list are of different types -- float,int, strings.How
do I write it into a csv file so that my output csv file looks like
1.2,abc,3
1.2,werew,4
.
.
.
1.4,qew,2
Answer: Python's built-in [CSV module](http://docs.python.org/2/library/csv.html) can
handle this easily:
import csv
with open("output.csv", "wb") as f:
writer = csv.writer(f)
writer.writerows(a)
This assumes your list is defined as `a`, as it is in your question. You can
tweak the exact format of the output CSV via the various optional parameters
to `csv.writer()` as documented in the library reference page linked above.
|
Python Introspection: Defining dynamic class methods during runtime
Question: I'm trying to create a unit test, that checks that every function in
`mymodule` has its own `TestCase` instance.
To reduce boiler-plate code and manual effort I wanted to use
introspection/reflection to dynamically add `lambda` functions as class
methods to the initially empty class `Test_TestCases`.
The following code kind of works - it does indeed add lambdas as class methods
and `unittest.main()` finds and correctly calls them.
import unittest
from unittest import TestCase
import mymodule
class Test_TestCases(TestCase):
"""Class whose test_* methods will be created during runtime."""
pass
################################################################################
if __name__ == "__main__":
for item in dir(mymodule):
attr = getattr(pws, item)
if callable(attr):
testname = "Test_%s" % item
setattr(Test_TestCases, "test_%s_is_tested" % item,
lambda self: self.assertTrue(testname in globals()) and
issubclass(getattr(globals(), testname), TestCase))
unittest.main()
The problem is, that all tests succeed even though I do have untested
functions in my unit test module.
After a little trying around I figured out that the variable `testname` has
the same value every time the `lambda` is called.
I could minimize the problem to this piece of code for reproducability:
lambdas = []
for i in range(5):
lambdas.append(lambda: str(i))
print ", ".join(f() for f in lambdas)
I'd expect this output:
0, 1, 2, 3, 4
but instead I get:
4, 4, 4, 4, 4
It seems that the lambdas are initialized lazily.
Could anyone please explain this behaviour or give me a hint on how I would
accomplish my goal properly?
Thanks in advance
Answer: Shadow `testname` with another wrapper function:
def assertion(testname=testname):
def function(self):
return self.assertTrue(testname in globals()) and issubclass(getattr(globals(), testname), TestCase))
return function
setattr(Test_TestCases, "test_%s_is_tested" % item, assertion())
|
using cx_freeze on flask app
Question: I am using Flask to develop a python app. At the moment, I want this app to be
run locally. It runs locally fine through python, but when I use cx_freeze to
turn it into an exe for Windows, I can no longer use the
Flask.render_template() method. The moment I try to execute a render_template,
I get an http 500 error, exactly as if the html template I'm trying to render
does not exist.
The main python file is called index.py. At first I tried to run: `cxfreeze
index.py`. This did not include the "templates" directory from the Flask
project in the cxfreeze "dist" directory. So then I tried using this setup.py
script and running `python setup.py build`. This now includes the templates
folder and the index.html template, but I still get the http: 500 error when
it tries to render the template.
from cx_Freeze import setup,Executable
includefiles = [ 'templates\index.html']
includes = []
excludes = ['Tkinter']
setup(
name = 'index',
version = '0.1',
description = 'membership app',
author = 'Me',
author_email = '[email protected]',
options = {'build_exe': {'excludes':excludes,'include_files':includefiles}},
executables = [Executable('index.py')]
)
Here is an example method from the script:
@app.route('/index', methods=['GET'])
def index():
print "rendering index"
return render_template("index.html")
If I run `index.py` then in the console I get:
* Running on http://0.0.0.0:5000/
rendering index
127.0.0.1 - - [26/Dec/2012 15:26:41] "GET / HTTP/1.1" 200 -
127.0.0.1 - - [26/Dec/2012 15:26:42] "GET /favicon.ico HTTP/1.1" 404 -
and the page is displayed correctly in my browser, but if I run `index.exe`, I
get
* Running on http://0.0.0.0:5000/
rendering index
127.0.0.1 - - [26/Dec/2012 15:30:57] "GET / HTTP/1.1" 500 -
127.0.0.1 - - [26/Dec/2012 15:30:57] "GET /favicon.ico HTTP/1.1" 404 -
and
Internal Server Error
The server encountered an internal error and was unable to complete your request. Either the server is overloaded or there is an error in the application.
in my browser.
If I return raw html, e.g.
@app.route('/index', methods=['GET'])
def index():
print "rendering index"
return "This works"
then it works fine. So a possible work around is to stop using Flask's
templates and hardcode all the html logic into the main python file. This gets
very messy though, so I'd like to avoid it if possible.
I'm using Python 2.7 32-bit, Cx_freeze for Python 2.7 32-bit, and Flask 0.9
Thanks for any help and ideas!
Answer: After many false trails trawling through the Flask and Jinga modules, I
finally found the problem.
CXFreeze does not recognize that jinja2.ext is a dependency, and was not
including it.
I fixed this by including `import jinja2.ext` in one of the python files.
CXFreeze then added `ext.pyc` to library.zip\jinja. (Copying it in manually
after the build also works)
Just in case anyone else is mad enough to try use Flask to develop locally run
apps :)
|
How can module be visible from one import and not visible from another?
Question: So I've got an application that's using `pymysql`, the pure python mysql
client implementation. Before I go into my response, I'd like to stress the
fact that I am not open to using a different mysql driver.
I have a module implementing a data structure that's backed by MySQL. The gist
of the module is as follows:
import pymysql
class Whatever:
def __init__(self):
# Debug statement
print dir(pymysql)
# use the cursors submodule
self.conn = pymysql.connect( ... , cursorclass=pymysql.cursors.DictCursor)
When I import this in my test file, everything is fine. Here is the output of
the `print` statement. In particular, I draw your attention to the cursors
module:
['BINARY', 'Binary', 'Connect', 'Connection', 'DATE', 'DATETIME', 'DBAPISet', 'DataError',
'DatabaseError', 'Date', 'DateFromTicks', 'Error', 'FIELD_TYPE', 'IntegrityError',
'InterfaceError', 'InternalError', 'MySQLError', 'NULL', 'NUMBER', 'NotSupportedError',
'OperationalError', 'ProgrammingError', 'ROWID', 'STRING', 'TIME', 'TIMESTAMP', 'Time',
'TimeFromTicks', 'Timestamp', 'TimestampFromTicks', 'VERSION', 'Warning', '__all__',
'__builtins__', '__doc__', '__file__', '__name__', '__package__', '__path__',
'__version__', 'apilevel', 'charset', 'connect', 'connections', 'constants', 'converters',
'cursors', 'err', 'escape_dict', 'escape_sequence', 'escape_string', 'get_client_info',
'install_as_MySQLdb', 'paramstyle', 'sys', 'thread_safe', 'threadsafety', 'times', 'util',
'version_info']
When I import the module from my main file, I get an `AttributeError`:
Traceback (most recent call last):
File "xxx.py", line 72, in <module>
passwd='', db='test_db')
File "yyy.py", line 26, in __init__
passwd=passwd, db=db, cursorclass=pymysql.cursors.DictCursor)
AttributeError: 'module' object has no attribute 'cursors'
The output of the `dir` print is as follows:
['BINARY', 'Binary', 'Connect', 'Connection', 'DATE', 'DATETIME', 'DBAPISet',
'DataError', 'DatabaseError', 'Date', 'DateFromTicks', 'Error', 'FIELD_TYPE',
'IntegrityError', 'InterfaceError', 'InternalError', 'MySQLError', 'NULL', 'NUMBER',
'NotSupportedError', 'OperationalError', 'ProgrammingError', 'ROWID', 'STRING', 'TIME',
'TIMESTAMP', 'Time', 'TimeFromTicks', 'Timestamp', 'TimestampFromTicks', 'VERSION',
'Warning', '__all__', '__builtins__', '__doc__', '__file__', '__name__', '__package__',
'__path__', '__version__', 'apilevel', 'charset', 'connect', 'constants', 'converters',
'err', 'escape_dict', 'escape_sequence', 'escape_string', 'get_client_info',
'install_as_MySQLdb', 'paramstyle', 'sys', 'thread_safe', 'threadsafety', 'times',
'version_info']
Notably, `cursors` is absent. Checking `pymysql.__file__` is the same in both
cases, and the output is:
__init__.py charset.py connections.py constants converters.pyc cursors.pyc err.pyc times.py util.py
__init__.pyc charset.pyc connections.pyc converters.py cursors.py err.py tests times.pyc util.pyc
Clearly `cursors.py` is there. So what gives?
Answer: You need to add an explicit `import pymysql.cursors` at the top of your file.
the `cursors` subpackage is not listed in the `pymysql`'s `__all__` and thus
isn't imported when you do just `import pymysql`.
|
NameError: name 'Game' is not defined, but it is
Question: I am learning python using the book _Learn python the hard way_. I am doing
one of the exercises, which contains many if loop's. I met an error which says
`Game` is not defined, but I did define it before. Anyone ideas?
from sys import exit
from random import randint
class Game(object):
def __init__(self, start):
self.quips = [
"You died. You kinda suck at this.",
"Nice job, you died ... jackass.",
"Such a luser.",
"I have a small puppy that's better at this."]
slef.start = start
def play(self):
next = self.start
while True:
print "\n-------"
room = getattr(self, next)
next = room()
def death(self):
print self.quips[randint(0, len(quips)-1)]
exit(1)
def central_corridor(self):
print "The Gothons of Planet Percal #25 have invaded your ship and destroyed"
print "your entire crew. You are the last surviving member and your last"
print "mission is to get the neutron destrut bomb from the Weapons Armory,"
print "put it in the bridge, and blow the ship up after getting into an "
print "escapr pod."
print "\n"
print "You're running down the central corridor to the Weapons Armory when"
print "a Gothon jumps out, red scaly skin, dark grimy teeth, and evil clown costume"
print "flowing around his hate filled body. He's blocking the door to thr"
print "Armory and about to pull a weapon to blast you."
action =raw_input("> ")
if action == "shoot!":
print "Quick on the draw you yank out your blaster and fire it at the Gothan."
print "His clown costume is flowing and moving around his body, which throws"
print "off your aim. Your laser hits new costume but misses him entirely. This"
print "completely ruins his brand new costumr his mother bought him, which"
print " makes him fly into an insane rage and blast you repeatedly in the face until"
print "you are dead. Then he eats you."
return 'death'
elif action =="dodge!":
print "Like a world class boxer you dodge, weave, slip and slide right"
print "as the Gothon's blaster cranks a laser past your head."
print "In the middle of your artful dodge your foot slips and you"
print "You wake up shortly after only to die as the Gothon stomps on"
print "your head and eats you."
return 'death'
elif action =="tell a joke":
print "Lucky for you they made you learn Fothon insults in the acsdemy."
print "You tell teh one Gothon k=joke you know:"
print "Lbhe zbgure vf fb sng, jura fur fvgf nebhag gur ubhfr, fur fvgf nrbhaq"
print "The Gothon stops, tries not to laugh, then busts out laughing and can't"
print "While he's laughing you run up and shoot him square in the head"
print "putting hm down, then jump through the Weapon Armory door."
return 'laser_weapon_asmory'
else:
print "DOES NOT COMPUTE!"
return 'central_corridor'
def laser_weapon_armory(self):
print " You do a dive roll into the Weapon Armory, crough and scan the room"
print "for more Gothans that might be hiding. It's dead quiet, too quiet."
print "You stand up and run to the far side of the room and find the"
print "neutron bomb in its container. There's a keypad lock on the code"
print "and you need the code to get the bomb out. If you get the code"
print "wrong 10 times then the lock closes forever and you can't"
print "get the bomb. The code is 3 digits."
code = "%d%d%d" % (randint(1,9), randint(1,9), randint(1,9))
guess = raw_input("[keypad]> ")
guesses = 0
while guess != code and guesses < 10:
print "BZZZZEDDD!"
guesses += 1
guess = raw_input("[keypad]> ")
if guess == code:
print "The container clicks open and the seal breaks, letting gas out."
print "You grab the neutron bomb and run as fast as you can to the"
print "bridge where you must place it in the right spot."
return 'the_bridge'
else:
print "The lock buzzes one last time and then you hear s sickening"
print "melting sound as teh mechanism is fused together."
print "You decide to sit there, and finally the Gothons blow up the"
return 'death'
def the_bridge(self):
print "You burst onto the Brisge with the netron destruct bomb"
print "under your arm and surprise 5 Gothon who are trying to"
print "take control of the ship. Each of them has an even uglier"
print "clown costume than the last. They haven't pulled their"
print "weapons out yet, as they see the active bomb under your"
print "arm and don't want to see it off."
action = raw_input("> ")
if action == "throw the bomb":
print "In a panic you throw the bomb at the group of Gothons"
print "and make a leap for the door. Right as you drop it a"
print "Gothon shoots you right in the back kiling you."
print "As you die you see another Gothon frantically try to disarm"
print "the bomb. You die knowing they will probably blow up when"
print "it goes off."
return 'death'
elif action == "slowly place the bomb":
print "You point your blaster at teh bomb under your arm"
print "and the Gothons put their hand up and start to sweat."
print "You inch backwark to the door, open it, and then carefully"
print "place the bomb on the floor, pointing your blaster at it."
print "You then jump back through the door, punch the close button"
print "and blast the lock so the Gothons can't get out."
print "Now that the bomb is placed you run to the escape pod to"
print "get off this tin can."
return 'escapr_pod'
else:
print "DOES NOT COMPUTE!"
return "the_brigde"
def escape_pad(self):
print "You rush through the ship desperately trying to make it to"
print "the escape pod before the whole ship explodes. It seemd like"
print "hardly any Gothons are on the ship, so your run is clear of"
print "interference. YOu get to the chamber with the excape pod, and"
print "now need to pick one to take. Some of them could be damaged"
print "but you don't have time to look. There's 5 pots, which one"
print "do you take?"
good_pod = randint(1,5)
guess = raw_input("[pod #]> ")
if int(guess) != good_pod:
print "You jump into pod %s and hit the eject button." % guess
print "The pod escaped out into the void of space, then"
print "implodes as the hull ruptures, crushing your body"
print "into jam jelly."
else:
print "You jump into pod %s and hit the eject button." % guess
print "The pod eadily slides out into space heading to"
print "the planet below. As it flies to the planet, you look"
print "back and see your ship implode then explode like a"
print "bright star, taking out the Gothon ship at the same"
print "time. You won!"
exit(0)
a_game = Game("central_corridor")
a_game.play()
Answer: I think this is the result of an indentation error. In your posted code, you
have
class Game(object):
def __init__(self, start):
[...]
print "time. You won!"
exit(0)
a_game = Game("central_corridor")
a_game.play()
So that you're defining `a_game` _inside_ the `Game` class, when `Game` isn't
defined yet. Shift it to the left to move it outside the `Game` scope, i.e.
a_game = Game("central_corridor")
a_game.play()
(on the same level as `class Game(object):`).
|
Parsing html in Python 2.7 with regex - don't really understand that
Question: Sorry for being kinda dumb, but I really need help in Python.
['<a href="needs to be cut out">Foo to BAR</a>', '<a href="this also needs to be cut out">BAR to Foo</a>']
So I have this tuple, and I need to cut out what's inside that href attribute
and what's inside `<a>` tag - basically, I want to get a tuple that looks
like:
[["needs to be cut out", "Foo to BAR"], ["this also needs to be cut out", "BAR to Foo"]]
inside href attribute there are a lot of special symbols for example,
<a href="?a=p.stops&direction_id=23600&interval=1&t=wml&l=en">
As I think, there's too much trouble in using HTML parsers if I really don't
need to try to parse the object tree but only need a few url's and words from
the webpage. But I can't really understand how to form regexes. Regexes that I
formed seem to be completely wrong. So I'm asking if somebody could help me
with it.
Answer: Just use a HTML parser anyway. Python comes with a few included, and the
[`xml.etree.ElementTree`
API](http://docs.python.org/2/library/xml.etree.elementtree.html) is easier to
get working than a regular expression for even simple `<a>` tags with
arbitrary attributes:
from xml.etree import ElementTree as ET
texts = []
for linktext in linkslist:
link = ET.fromstring(linktext)
texts.append([link.attrib['href'], link.text])
If you use `' '.join(link.itertext())` you can get the text out of _anything_
nested under the `<a>` tag, if you find that some of the links have nested
`<span>`, `<b>`, `<i>` or other inline tags to mark up the link text further:
for linktext in linkslist:
link = ET.fromstring(linktext)
texts.append([link.attrib['href'], ' '.join(link.itertext())])
This gives:
>>> from xml.etree import ElementTree as ET
>>> linkslist = ['<a href="needs to be cut out">Foo to BAR</a>', '<a href="this also needs to be cut out">BAR to Foo</a>']
>>> texts = []
>>> for linktext in linkslist:
... link = ET.fromstring(linktext)
... texts.append([link.attrib['href'], ' '.join(link.itertext())])
...
>>> texts
[['needs to be cut out', 'Foo to BAR'], ['this also needs to be cut out', 'BAR to Foo']]
|
Gdata API Installation
Question: I have no idea what I'm doing. I'm using Python 2.7 on OSX with the Eclipse
PyDev IDE. I've never worked with an API before, but I need to use the google
calendar API with a Python application I'm developing. I downloaded the latest
gdata module from Google and installed it using this line in Terminal while in
the directory into which I downloaded the gdata folder (Downloads):
sudo python setup.py install
It seemed to install everything into a Python directory deep within my
machine's Library, no errors were given. However, now when I attempt to run a
program with the following import commands:
import gdata.calendar.data
import gdata.calendar.client
import gdata.acl.data
import atom
I get the following error:
ImportError: No module named gdata.calendar.data
Clearly indicating I have done something wrong on the install. Thoughts?
Answer: It's probably installed, but you haven't told Eclipse where to look for
`gdata`.
Right click on the project in Eclipse and choose `Properties -> PyDev -
PYTHONPATH -> Source Folders` and click "Add source folder".
The folder will (probably) be in `/Library/Python/2.7/site-packages/gdata`,
depending on the version and where you installed it. It might be somewhere
else, like `dist-packages` instead of `site-packages`, but once you find it
and add the folder inside Eclipse, the imports should work.
**Edit** : Don't forget to do the same for `atom`, too.
|
Retrieve Only the last values of a row in SQLITE with python 27
Question: I'm using this code to get all data from a sqlite row, but I would like to
retrieve only the last 30 entries.
import sqlite3
from matplotlib import pyplot
fig = pyplot.figure()
con = sqlite3.connect('growll.db')
con.text_factory = str
cur = con.cursor()
cur.execute("select temp from GrowLLDados")
ar=[r[0] for r in cur.fetchall()]
Answer: something like `"select temp from GrowLLDados ORDER BY id DESC LIMIT 30"`
where `id` is an auto-incrementing counter or at least means the higher the
number the more recent the entry ...
|
Search for words (exact matches) in multiple texts using Python
Question: I want to let the user choose and open multiple texts and perform a search for
exact matches in the texts. I want the encoding to be unicode.
If I search for "cat" I want it to find "cat", "cat,", ".cat" but not
"catalogue".
I don't know how to let the user search for two words ("cat" OR "dog") in all
of the texts at the same time?????? Maybe I can use RE?
So far I have just made it possible for the user to insert the path to the
directory containing the text files to search in. Now I want to let the user
(raw_input) search for two words in all of the texts, and then print and save
the results (e.g. "search_word_1" and "search_word_2" found in document1.txt,
"search_word_2" found in document4.txt) in a separate document (search_words).
import re, os
path = raw_input("insert path to directory :")
ex_library = os.listdir(path)
search_words = open("sword.txt", "w") # File or maybe list to put in the results
thelist = []
for texts in ex_library:
f = os.path.join(path, texts)
text = open(f, "r")
textname = os.path.basename(texts)
print textname
for line in text.read():
text.close()
Answer: You need to split the text in each file on whitespace and punctuation. Once
that's done you can simply look for the words you are searching for in the
remaining list. You also need to convert everything to lowercase, unless you
also want case sensitive search.
|
Python - Returning max number in an array. Errors
Question: I have a Python script that connects to a website via FTP and lists the
current version numbers of programs located on the website. I created an array
to hold the version numbers till the script would pick the largest number out
of the array and tell me what it was. For example my array would usually look
like this:
array = ['1.04','1.6','1.14']
So I used...
max_in_array = max(array)
to return the largest value in the array.
Unfortunately, I received '1.6' as the largest number when, in fact, '1.14' is
the latest version number. The only other thing I could think to do is to cut
off the '1.' from the list of arrays so that I receive:
array = ['04','6','14']
And then paste it back on to get the full version number. But since this
website contains many versions such as '2.02.04' and '1.14.01' I don't know
how to efficiently do that.
Any help would be greatly appreciated!
* * *
os.chdir("./gnu/"+_package)
pope = len(_package) + 1 ## Cuts off name of program
char = len(_package) - 12 ## Cuts off extension ".tar.gz"
for tok in glob.glob("*.tar.gz"):
token.append(tok) ## Appends name to array
bork = max(token) ## Gets max version number (sometimes useless)
print bork
char = len(bork) - 7
for _gnu in glob.glob("*.tar.gz"): ## Finds only matches with .tar.gz
_gnuapp.append(_gnu[pope:char]) ## Appends version number to array
spoke = max(_gnuapp) ## Gets max version number
_ver = _package + "-" + spoke + ".tar.gz" ## Compiles the package name, ver #, and extension
_down(_user, _ver, _package) ## Opens information in download module
Answer: **Edit:** Sorry, misinterpreted the question at first - see [this
answer](http://stackoverflow.com/questions/1714027/version-number-comparison)
for a few methods regarding comparing version numbers. Taking the second
answer in there (which suggests using `distutils.version`'s `StrictVersion`),
you can try this:
In [3]: from distutils.version import StrictVersion
In [4]: s = ['1.04','1.6','1.14', '2.02.04', '1.14.01']
In [5]: max(s, key=StrictVersion)
Out[5]: '2.02.04'
* * *
One thing to note is that you are actually comparing strings and not numbers.
One thing you can do to ensure that you are comparing the number themselves
(disregarding that you want to do with the item afterwards) is to provide a
key to the `max` function:
In [1]: s = ['1.04','1.6','1.14']
In [2]: max(s, key=float)
Out[2]: '1.6'
Since you are looking to compare float values (and not the strings), this
compares the float equivalents of the strings. However it may be best to
convert those to floats before proceeding:
In [4]: s = ['1.04','1.6','1.14']
In [5]: s_floats = [float(x) for x in s]
In [6]: s_floats
Out[7]: [1.04, 1.6000000000000001, 1.1399999999999999]
You can then use max as you expect:
In [9]: max(s_floats)
Out[9]: 1.6000000000000001
|
adding noise to a signal in python
Question: I want to add some random noise to some 100 bin signal that I am simulating in
Python - to make it more realistic.
On a basic level, my first thought was to go bin by bin and just generate a
random number between a certain range and add or subtract this from the
signal.
I was hoping (as this is python) that there might a more intelligent way to do
this via numpy or something. (I suppose that ideally a number drawn from a
gaussian distribution and added to each bin would be better also.)
Thank you in advance of any replies.
* * *
I'm just at the stage of planning my code, so I don't have anything to show. I
was just thinking that there might be a more sophisticated way of generating
the noise.
In terms out output, if I had 10 bins with the following values:
Bin 1: 1 Bin 2: 4 Bin 3: 9 Bin 4: 16 Bin 5: 25 Bin 6: 25 Bin 7: 16 Bin 8: 9
Bin 9: 4 Bin 10: 1
I just wondered if there was a pre-defined function that could add noise to
give me something like:
Bin 1: 1.13 Bin 2: 4.21 Bin 3: 8.79 Bin 4: 16.08 Bin 5: 24.97 Bin 6: 25.14 Bin
7: 16.22 Bin 8: 8.90 Bin 9: 4.02 Bin 10: 0.91
If not, I will just go bin-by-bin and add a number selected from a gaussian
distribution to each one.
Thank you.
* * *
It's actually a signal from a radio telescope that I am simulating. I want to
be able to eventually choose the signal to noise ratio of my simulation.
Answer: You can generate a noise array, and add it to your signal
import numpy as np
noise = np.random.normal(0,1,100)
# 0 is the mean of the normal distribution you are choosing from
# 1 is the standard deviation of the normal distribution
# 100 is the number of elements you get in array noise
|
overlay a smaller image on a larger image python OpenCv
Question: Hi I am creating a program that replaces a face in a image with someone else's
face. However, I am stuck on trying to insert the new face into the original,
larger image. I have researched ROI and addWeight(needs the images to be the
same size) but I haven't found a way to do this in python. Any advise is
great. I am new to opencv.
I am using the following test images:
smaller_image:
larger_image:
Here is my Code so far... a mixer of other samples:
import cv2
import cv2.cv as cv
import sys
import numpy
def detect(img, cascade):
rects = cascade.detectMultiScale(img, scaleFactor=1.1, minNeighbors=3, minSize=(10, 10), flags = cv.CV_HAAR_SCALE_IMAGE)
if len(rects) == 0:
return []
rects[:,2:] += rects[:,:2]
return rects
def draw_rects(img, rects, color):
for x1, y1, x2, y2 in rects:
cv2.rectangle(img, (x1, y1), (x2, y2), color, 2)
if __name__ == '__main__':
if len(sys.argv) != 2: ## Check for error in usage syntax
print "Usage : python faces.py <image_file>"
else:
img = cv2.imread(sys.argv[1],cv2.CV_LOAD_IMAGE_COLOR) ## Read image file
if (img == None):
print "Could not open or find the image"
else:
cascade = cv2.CascadeClassifier("haarcascade_frontalface_alt.xml")
gray = cv2.cvtColor(img, cv.CV_BGR2GRAY)
gray = cv2.equalizeHist(gray)
rects = detect(gray, cascade)
## Extract face coordinates
x1 = rects[0][3]
y1 = rects[0][0]
x2 = rects[0][4]
y2 = rects[0][5]
y=y2-y1
x=x2-x1
## Extract face ROI
faceROI = gray[x1:x2, y1:y2]
## Show face ROI
cv2.imshow('Display face ROI', faceROI)
small = cv2.imread("average_face.png",cv2.CV_LOAD_IMAGE_COLOR)
print "here"
small=cv2.resize(small, (x, y))
cv2.namedWindow('Display image') ## create window for display
cv2.imshow('Display image', small) ## Show image in the window
print "size of image: ", img.shape ## print size of image
cv2.waitKey(1000)
Answer: A simple way to achieve what you want:
import cv2
s_img = cv2.imread("smaller_image.png")
l_img = cv2.imread("larger_image.jpg")
x_offset=y_offset=50
l_img[y_offset:y_offset+s_img.shape[0], x_offset:x_offset+s_img.shape[1]] = s_img
## Update
I suppose you want to take care of the alpha channel too. Here is a quick and
dirty way of doing so:
s_img = cv2.imread("smaller_image.png", -1)
for c in range(0,3):
l_img[y_offset:y_offset+s_img.shape[0], x_offset:x_offset+s_img.shape[1], c] =
s_img[:,:,c] * (s_img[:,:,3]/255.0) + l_img[y_offset:y_offset+s_img.shape[0], x_offset:x_offset+s_img.shape[1], c] * (1.0 - s_img[:,:,3]/255.0)
|
Django output html time is 8 hours ahead of database time
Question: I'm very new to **Django** and I've been learning the framework from the book
_"Practical django Projects"_ (the book teaches us to write a cms). My code
runs fine, but I have time problem with the `get_absolute_url` function below.
It's actually outputting the link 8 hours ahead of the time saved in my
database. I used python shell to look at the saved time in the database and
the time saved in the admin interface, they are all correct. But when I use
the `get_absolute_url func` below to generate the link in browser, it becomes
8 hours ahead and throws the day off. I set the correct zone in my Django
setting file. I cannot figure out what's wrong.
How I can fix this (I'm using sqlite3 for my database, Django 1.4.1)?
Here is my code for the Entry class:
import datetime
from django.db import models
from django.contrib.auth.models import User
from tagging.fields import TagField
from markdown import markdown
from django.conf import settings
from django.utils.encoding import smart_str
class Entry(models.Model):
live = LiveEntryManager()
objects = models.Manager()
#define constant options
LIVE_STATUS = 1
DRAFT_STATUS = 2
HIDDEN_STATUS = 3
STATUS_CHOICES = (
(LIVE_STATUS, 'Live'),
(DRAFT_STATUS,'Draft'),
(HIDDEN_STATUS, 'Hidden'),
)
#adding features to admin interface
class Meta:
ordering = ['-pub_date']
verbose_name_plural = "Entries"
#define model fields:
title = models.CharField(max_length=250)
excerpt = models.TextField(blank=True) #It's ok to not add anything for this field
body = models.TextField()
pub_date = models.DateTimeField(default=datetime.datetime.now())
slug = models.SlugField(unique_for_date='pub_date')
enable_comments = models.BooleanField(default=True)
featured = models.BooleanField(default=False)
status = models.IntegerField(choices=STATUS_CHOICES, default=LIVE_STATUS)
#HTML
excerpt_html = models.TextField(editable=False, blank=True)
body_html = models.TextField(editable=False, blank=True)
#third party:
tag = TagField()
#relationship fields:
categories = models.ManyToManyField(Category)
author = models.ForeignKey(User)
#define methods:
def save(self, force_insert=False, force_update=False):#modify the model.save() method
self.body_html = markdown(self.body)
if self.excerpt:
self.excerpt_html = markdown(self.excerpt)#from excerpt field to excerpt_html
super(Entry, self).save(force_insert, force_update)
def get_absolute_url(self):
return "%s" % self.pub_date.strftime("year:%Y/day:%d/hour:%H/minute:%M/second:%S")
#@models.permalink
#def get_absolute_url(self):
#return ('coltrane_entry_detail', (), {'year': self.pub_date.strftime("%Y"),
'month': self.pub_date.strftime("%b").lower(),
'day': self.pub_date.strftime("%d"),
'slug': self.slug})
def __unicode__(self):
return self.title
This is my entry_archive.html:
{% extends "base_entries.html"%}
{%block title%}{{block.super}} | Latest entries{% endblock %}
{% block content %}
{% for entry in latest %}
<h2>{{entry.title}}</h2>
<p>Published on {{ entry.pub_date|date:"F j P s, Y" }}</p>
{% if entry.excerpt_html%}
{{entry.excerpt_html|safe}}
{% else %}
{{entry.body_html|truncatewords_html:"50"|safe}}
{% endif%}
<p><a href="{{entry.get_absolute_url}}">Read full entry ...</a></p>
{% endfor %}
{%endblock%}
{%block whatis%}
<p>This is a list of the latest {{latest.count}} entries published in my blog.</p>
{% endblock %}
I couldn't post screenshot because i'm a new user. {{ entry.pub_date|date:"F j
P s, Y" }} in my html give me correct time: December 28 11:24 a.m. 45, 2012.
But {{entry.get_absolute_url}} gives me
year:2012/day:28/hour:19/minute:24/seconds:45
I add the () to pub_date =
models.DateTimeField(default=datetime.datetime.now()) as you guys suggested,
but the result is still the same(the book actually suggests not to add () ).
The thing troubles me is that {{ entry.pub_date|date:"F j P s, Y" }} gives me
the correct time on my html, but {{entry.get_absolute_url}} is 8 hours ahead.
I set my setting.py time zone to TIME_ZONE = 'America/Los_Angeles'. Thanks for
all the quick response, but this is killing me...
Answer: change the following:
pub_date = models.DateTimeField(default=datetime.datetime.now)
to Either
pub_date = models.DateTimeField(default=datetime.datetime.now())
or
pub_date = models.DateTimeField(auto_now_add=True)
|
Convert number to Italian and Italian to number in python
Question: I need Python code to convert numbers to and from Italian.
Looking at previous questions I learned that pynum2word does one way (num ->
words) in several languages but alas, not in Italian.
If no such code exist in Python, I wouldn't mind translating such code from
Perl/Ruby/Java.
Thanks.
Answer: To do the conversion from italian to number it's pretty simple using regexes:
import re
NUMBERS_SEQ = (
('dieci', '10'),
('undici', '11'),
('dodici', '12'),
('tredici', '13'),
('quattordici', '14'),
('quindici', '15'),
('sedici', '16'),
('diciasette', '17'),
('diciotto', '18'),
('diciannove', '19'),
('venti', '20'),
('trenta', '30'),
('quaranta', '40'),
('cinquanta', '50'),
('sessanta', '60'),
('settanta', '70'),
('ottanta', '80'),
('novanta', '90'),
('cento', '100'),
('mille', '1000'), ('mila', '1000'),
('milione', '1000000'), ('milioni', '1000000'),
('miliardo', '1000000000'), ('miliardi', '1000000000'),
('uno', '1'), ('un', '1'),
('due', '2'),
('tre', '3'),
('quattro', '4'),
('cinque', '5'),
('sei', '6'),
('sette', '7'),
('otto', '8'),
('nove', '9'),
)
NUMBERS = dict(NUMBERS_SEQ)
TOKEN_REGEX = re.compile('|'.join('(%s)' % num for num, val in NUMBERS_SEQ))
def normalize_text(num_repr):
'''Return a normalized version of *num_repr* that can be passed to let2num.'''
return num_repr.lower().translate(None, ' \t')
def let2num(num_repr):
'''Yield the numeric representation of *num_repr*.'''
result = ''
for token in (tok for tok in TOKEN_REGEX.split(num_repr) if tok):
try:
value = NUMBERS[token]
except KeyError:
if token not in ('di', 'e'):
raise ValueError('Invalid number representation: %r' % num_repr)
continue
if token == 'miliardi':
result += '0'*9
elif token in ('mila','milioni'):
zeros = '0' * value.count('0')
piece = result[-3:].lstrip('0')
result = (result[:-len(piece)-len(zeros)] +
piece +
zeros)
elif not result:
result = value
else:
length = len(value)
non_zero_values = len(value.strip('0'))
if token in ('cento', 'milione', 'miliardo'):
if result[-1] != '0':
result = (result[:-length] +
result[-1] +
'0' * value.count('0'))
continue
result = (result[:-length] +
value.rstrip('0') +
result[len(result) -length + non_zero_values:])
return add_thousand_separator(result)
def add_thousand_separator(s, sep='.'):
'''Return the numeric string s with the thousand separator.'''
rev_s = s[::-1]
tokens = [rev_s[i:i+3][::-1] for i in range(0, len(s), 3)][::-1]
return sep.join(tokens)
Result:
>>> let2num('unmilione')
'1.000.000'
>>> let2num('unmilionemilleduecento')
'1.001.200'
>>> let2num('unmilionemilleduecentotre')
'1.001.203'
>>> let2num('ventiquattro')
'24'
>>> let2num(normalize_text('Dieci milioni e CentoQuarantaTreMila miliardi di miliardi di miliardi Otto cento e quattro'))
'10.143.000.000.000.000.000.000.000.000.000.804'
>>> let2num('ventiquattromiliardicentotrentatremilionitredicimiladuecentouno')
'24.133.013.201'
Note that you must spell the number correctly. In the last example if you put
in input the string: `'...centotrentatremilione...'`, with the
(_wrong_)singular `milione` instead of `milioni` you get:
>>> let2num('ventiquattromiliardicentotrentatremilionetredicimiladuecentouno')
'24.003.013.201'
Which is not "correct". But the spelling is actually wrong. I believe it
shouldn't be too hard to allow `milione` as exact synonim for `milioni`, or to
do add some error checking such that it would raise an error if it finds an
incorrect spelling. Just be aware of this.
As a suggestion for debugging the above code(if you want to make changes) is
to add a line like:
print 'token:', token, 'current result:', result
As first instruction of the `for` loop. Then watching what is being done you
should be able to recognize the "reasoning" behind the code and see where the
bug lays.
I think for the other conversion it'd be easy to implement something based on
`pynum2word`. If you don't know italian I may try to help writing it.
|
Looping and Naming Variables in Python Bar Chart
Question: I'm using matplotlib in Python to create a stacked bar chart showing order
volume over the course of the day by hour, versus a calendar equivalent day
last year.
I've already arranged an array that includes today's and last year's order
volume:
allorders=[(23, 28), (15, 7), (15, 5), (8, 9), (4, 2), (5, 3), (4, 6), (8, 10), (28, 24), (45, 46), (55, 65), (0, 74), (0, 64), (0, 58), (0, 62), (0, 62), (0, 42), (0, 43), (0, 38), (0, 39), (0, 32), (0, 40), (0, 41), (0, 16)]
For stacked bars, you would normally use the following syntax:
import matplotlib.pyplot as plt
import numpy as np
n=2
ind = np.arange(n)
width = 0.35
plt.ylabel('Orders')
plt.xticks(ind+width/2., ('Today', 'Last Year on Calendar Equivalent'))
plt.yticks(np.arange(0,plottotal,10))
p1= plt.bar(ind, allorders[0], width, color='#000099')
p2= plt.bar(ind, allorders[1], width, color='#000099', bottom=allorders[0])
however, this can be daunting with large amount of stacked charts. Therefore,
I'm trying to create a loop to go through the 'allorders' array and stack them
via:
for i in allorders:
if i=0:
p1=plt.bar(ind, allorders[i], width, color='#000099')
bottomcounter=allorders[i]
else:
'p+i' = plt.bar(ind, allorders[i], width, color='r', bottom=bottomcounter)
bottomcounter=bottomcounter+allorders[i]
but, I get all sorts of errors, including that the clause 'if i=0' has invalid
syntax, and that 'p+i'cannot be used to auto-name variables.
So, SO wizards:
1) how do you name new variables automatically in a loop (so when i=0, the
variable is named p0, when i=1, the variable is named p1, etc.)
2) what's wrong with including the 'if i=0' clause?
Since I'm new to Python (coming from R and Stata), please treat me like an
infant, with step-by-step code if you can!
Thanks!
Answer: To start with, you need to read and understand the official
[tutorial](http://docs.python.org/2/tutorial/).
Second, to fix your code:
import itertools
allorders=[(23, 28), (15, 7), (15, 5), (8, 9), (4, 2), (5, 3), (4, 6), (8, 10), (28, 24), (45, 46), (55, 65), (0, 74), (0, 64), (0, 58), (0, 62), (0, 62), (0, 42), (0, 43), (0, 38), (0, 39), (0, 32), (0, 40), (0, 41), (0, 16)]
width = .35
plts = []
colors = ['k','r','b']
for i,order in enumerate(allorders):
bottom_counter = 0
loc_plts = []
for o,c in zip(order,itertools.cycle(colors)):
tmp_plt = plt.bar(i, o, width, color=c, bottom=bottom_counter)
loc_plts.append(tmp_plt)
bottom_counter+=o
plts.append(loc_plts)
|
Subprocess: Execute two or more preexec_fn
Question: I was wondering if there is a way of creating a
[subprocess](http://docs.python.org/2/library/subprocess.html) (through
`subprocess.Popen`) that calls secuentially two (or more) `preexec_fn`.
For instance, calling `setegid` and `seteuid` (just for example purposes).
So far, I found this workaround (and well... it works, but it doesn't look
too... direct or "clean")
#!/usr/bin/python2.7
import subprocess
import os
def preExecuter(listOfFunctions):
for functionEntry in listOfFunctions:
functionEntry["function"](* functionEntry.get("args", []), **functionEntry.get("kwargs", {}))
listOfFunctions = [
{
"function": os.setegid,
"args": [1000],
},
{
"function": os.seteuid,
"args": [1000],
},
]
if __name__ == "__main__":
sp = subprocess.Popen(["whoami"], preexec_fn=preExecuter(listOfFunctions))
sp.communicate()
Is there a better way of doing this? Thank you in advance.
Answer: That's not even going to work, since the call to preExecuter actually executes
the setegid and seteuid operations, and is done before Popen is called. What's
wrong with
def my_pre_exec() :
os.setegid(1000)
os.seteuid(1000)
subprocess.Popen( ..., preexec_fn = my_pre_exec )
|
Python 3 parsing iTunes library plist file using plistlib
Question: I'm trying to parse a iTunes media library file, which is a plist file using
python & plistlib. I wrote a simple python script:
import plistlib
plist = plistlib.readPlist('tunes.xml')
print(plist['Tracks'])
But when I try and run it an error occurs on line 3:
UnicodeEncodeError: 'ascii' codec can't encode character '\xe9' in position 21970: ordinal not in range(128)
I've tried to load the file with a utf-8 encoding convert to a `bytearray` and
use `plistlib.readPlistFromBytes` but still the error occurs
Which is the best way to fix this?
Answer: Chances are the terminal session or console you're running this in is not set
to a UTF-8 compatible `locale`. See
<https://wiki.archlinux.org/index.php/Locale> for more info. For example, in
US English locales:
export LANG=en_US.UTF-8
|
Django 1.4 on GAE: sqlite "ImportError: cannot import name utils"
Question: I'm trying to get sqlite3 support working on Django 1.4 on Google App Engine
1.7.4 on Python 2.7.
I fiddled around with the "Google Cloud SQL" database backend, all worked well
(syncdb, insert/update/delete, ...).
But then I enabled sqlite (as Google Cloud SQL is slow when on localhost):
import os
if (os.getenv('SERVER_SOFTWARE', '').startswith('Google App Engine') or
os.getenv('SETTINGS_MODE') == 'pushtolive'):
# Running on production App Engine, so use a Google Cloud SQL database.
DATABASES = {
'default': {
'ENGINE': 'google.appengine.ext.django.backends.rdbms',
'INSTANCE': 'xyz:xyz',
'NAME': 'my_database',
}
}
else:
# Running in development, so use a local SQLite database
DATABASES = {
'default': {
'ENGINE': 'django.db.backends.sqlite3',
'NAME': '/tmp/mysite.db',
}
}
and when I open any url (e.g. 127.0.0.1:8080) then I run into [this monstrous
stack
trace](https://gist.github.com/raw/4405464/76f6a6c31fb56d54bc8e9668ddea40d508ea714c/sqlite.traceback).
I stripped down the stack trace so it's more readable:
ERROR 2012-12-29 09:07:06,223 base.py:215] Internal Server Error: /favicon.ico
Traceback (most recent call last):
File "/Users/philipp/python/mysite/urls.py", line 4, in <module>
from django.contrib import admin
File ".../google_appengine/lib/django_1_4/django/contrib/admin/__init__.py", line 3, in <module>
from django.contrib.admin.helpers import ACTION_CHECKBOX_NAME
File ".../google_appengine/lib/django_1_4/django/contrib/admin/helpers.py", line 2, in <module>
from django.contrib.admin.util import (flatten_fieldsets, lookup_field,
File ".../google_appengine/lib/django_1_4/django/contrib/admin/util.py", line 1, in <module>
from django.db import models
File ".../google_appengine/lib/django_1_4/django/db/__init__.py", line 40, in <module>
backend = load_backend(connection.settings_dict['ENGINE'])
File ".../google_appengine/lib/django_1_4/django/db/__init__.py", line 34, in __getattr__
return getattr(connections[DEFAULT_DB_ALIAS], item)
File ".../google_appengine/lib/django_1_4/django/db/utils.py", line 92, in __getitem__
backend = load_backend(db['ENGINE'])
File ".../google_appengine/lib/django_1_4/django/db/utils.py", line 24, in load_backend
return import_module('.base', backend_name)
File ".../google_appengine/lib/django_1_4/django/utils/importlib.py", line 35, in import_module
__import__(name)
File ".../google_appengine/lib/django_1_4/django/db/backends/sqlite3/base.py", line 14, in <module>
from django.db import utils
ImportError: cannot import name utils
From the stack trace I read that the execution runs to the `django.db.utils`
module, then into `django.db.backends.sqlite3.base`, then it tries to jump
into `django.db.utils` again but that then strangely fails.
The problem seems to be in the GAE environment, since this works:
python mysite/manage.py syncdb
And this as well:
python mysite/manage.py shell
>>> from django.contrib.auth.models import User
>>> u = User(username="hans")
>>> u.save()
>>> User.objects.all()
[<User: hans>]
**What I tried so far:**
* switched from/to Django 1.3/1.4
* [uninstalled GAE](http://stackoverflow.com/questions/9189054/how-do-i-uninstall-google-app-engine-sdk#answer-14081488), installed it again
* I tried through all the solutions google reveals for "ImportError from django.db import utils"
* there is [this similar question](http://stackoverflow.com/questions/7866256). I tried executing the statements in the question and I don't run into the problem.
I'm on OS X 10.8.2 My PYTHONPATH is
`:/usr/local/google_appengine:/usr/local/google_appengine/lib/django_1_4`
Answer: As it's [not good practice to use sqlite in dev and mysql (as used by Cloud
SQL) in production](http://stackoverflow.com/questions/2306048/django-sqlite-
for-dev-mysql-for-prod) I don't recommend this setup to anyone.
Then, there is the option `--use_sqlite`: This is used to speed up development
when using the Google Data*store*. There is no similar option for Cloud SQL.
|
Import error in pyzmq after updating libzmq
Question: I have an error when I attempt to update my ZeroMQ to the new version 3.2.
This is the ouput that I have:
Traceback (most recent call last):
File "<stdin>", line 1, in <module>
File "/usr/local/lib/python2.7/dist-packages/zmq/__init__.py", line 51, in <module>
from zmq import core, devices
File "/usr/local/lib/python2.7/dist-packages/zmq/core/__init__.py", line 26, in <module>
from zmq.core import (constants, error, message, context,
ImportError: /usr/local/lib/python2.7/dist-packages/zmq/core/socket.so: undefined symbol: zmq_sendmsg
I really don't know what's going on. I'm using Ubuntu 12.04 and I develop in
Python. I've already checked on Stack Overflow but I did not see anything. It
worked well before but I started to have this error after installing pyzmq
2.2.0.1.
Could anyone help me with this?
Thanks MAXA
Answer: As I [replied to you](http://lists.zeromq.org/pipermail/zeromq-
dev/2012-December/019868.html) on the zeromq-dev list, you must rebuild pyzmq
any time you do a major upgrade of libzmq.
|
Days of the week Django
Question: please, explain me, how do this thing: I have a week number (52, for example)
and year (2012). So, how I can get the days number (monday - 24, tuesday - 25,
etc). Yes, I read [this](http://docs.python.org/2/library/datetime.html), but
I cant understand, how to do it.
Thanks.
Answer: I would do it like this:
from datetime import date, timedelta
def get_weekdays(year, week):
january_first = date(year, 1, 1)
monday_date = january_first + timedelta(days=week * 7 - january_first.weekday())
# monday, tuesday, .. sunday
return [(monday_date + timedelta(days=d)).day for d in range(7)]
(my weeks start at monday)
|
How do you invoke a function on a bunch of lines selected via Ctrl-v?
Question: I am selecting some text via Ctrl-v (visual mode). Then I type \s to align
those lines and sort them like so:
"Strip trailing space
:map <Leader>S :1,$ s/\s\+$//g<CR>
:imap <Leader>S :1,$ s/\s\+$//g<CR>
How do I pass all the selected lines to Sort(). I thought the
**vim.current.range** object might do it but that didn't work out. Currently
the Sort() function reads text 1 line at a time via cr[0]. What I need to do
is store the split lines in a matrix, compute the required length/column and
print them out into the buffer.
function! Sort()
python << EOF
import vim
cr = vim.current.range
line = cr[0]
line = line.split()
fmt_str = ['%8s' for word in line]
fmt_str = ' '.join(fmt_str)
line = tuple([word for word in line])
print(fmt_str)
cr[0]= fmt_str % line
EOF
endfunction
"Sort and align
:map <Leader>s :call Sort()<CR>
Answer: When you want a mapping to work on the visual selection, you need to use
`:vnoremap`. An Ex command (like `:call`) will then automatically have the
visual range `'<,'>` prepended. An ordinary function would then be invoked
once per line, but you can define a special kind of function (cp. `:help
function-range-example`) that handles the range itself.
Since you seem to want to use Python, I'd just drop the prepended range via
`<C-u>` and access the selection's bounds via the `<` and `>` marks, then
access and modify the lines via `vim.current.buffer[lnum]`:
:vnoremap <Leader>s :<C-u>call Sort()<CR>
function! Sort()
...
start = vim.current.buffer.mark('<')[0]
end = vim.current.buffer.mark('>')[0]
|
Trouble with Apache, mod_wsgi, and Django configuration
Question: Just set up a 64 bit ubuntu EC2 instance using the Bitnami DjangoStack image.
So far I have installed a few python dependencies and removed the Project
django app which was created by default. I created a new app with 'django-
admin.py startproject projectname'. I then followed the instructions here:
<http://wiki.bitnami.org/Components/Django>, attempting to setup apache.
Here is my projectname.conf file:
Alias /static "/opt/bitnami/apps/django/lib/python2.7/site-packages/django/contrib/admin/static"
<Directory '/opt/bitnami/apps/django/lib/python2.7/site-packages/django/contrib/'>
Order allow,deny
Allow from all
</Directory>
WSGIScriptAlias /URL_mount_point "/opt/bitnami/apps/django/scripts/projectname.wsgi"
<Directory '/opt/bitnami/apps/django/scripts'>
Order allow,deny
Allow from all
</Directory>
Here is my projectname.wsgi
import os, sys
sys.path.append('/opt/bitnami/apps/django/django_projects')
sys.path.append('/opt/bitnami/apps/django/django_projects/projectname')
os.environ['DJANGO_SETTINGS_MODULE'] = 'projectname.settings'
import django.core.handlers.wsgi
application = django.core.handlers.wsgi.WSGIHandler()
Here are the last three lines of my httpd.conf:
Include "/opt/bitnami/apache2/conf/ssi.conf"
Include "/opt/bitnami/apache2/conf/bitnami/httpd.conf"
Include "/opt/bitnami/apps/django/conf/projectname.conf"
After doing this and restarting apache, hitting mydomain.com/projectname still
comes up with a 404 (the Bitnami landing page comes up just fine at
mydomain.com).
Am I missing something here? Are my paths in projectname.wsgi incorrect (I
have not strayed from the default Bitnami directory structure). Or is there
some additional step I am missing here?
Answer: You should be accessing:
http://mydomain.com/URL_mount_point
Since it appears you have not shown your original configuration, hard to say
whether that is the issue or whether is a typo of sorts.
|
Error running Pyserial
Question: I just installed Pyserial 2.6 and I have Python 2.7.3 unfortunately it either
did not install correctly or I am not using it correctly. I installed it
through terminal using the line
sudo easy_install pyserial
Unfortunately it gave me 2 warnings:
warning: no files found matching 'examples/miniterm.py'
warning: no files found matching 'test/test_io_lib.py'
Other than that it seemed to install correctly.
When I run this in Python I keep getting the farther below error
import serial
serial_input = serial.Serial('/dev/tty/.usbmodem3d241',9600)
while True:
ser.readline()
Error:
Traceback (most recent call last):
File "/Users/ben/Documents/Arduino_to_Python.py", line 5, in <module>
serial_input = serial.Serial('/dev/tty/.usbmodem3d241',9600)
File "build/bdist.macosx-10.7-intel/egg/serial/serialutil.py", line 261, in __init__
self.open()
File "build/bdist.macosx-10.7-intel/egg/serial/serialposix.py", line 278, in open
raise SerialException("could not open port %s: %s" % (self._port, msg))
SerialException: could not open port /dev/tty/.usbmodem3d241: [Errno 20] Not a directory: '/dev/tty/.usbmodem3d241'
Whatever serial port I try it never seems to work. I have tried the ones in
the Arduino program Tools>Serial Port and all of the prompts at
<http://pyserial.sourceforge.net/shortintro.html#opening-serial-ports>
Any help would be greatly appreciated. Thanks.
Answer: This `serial_input = serial.Serial('/dev/tty/.usbmodem3d241',9600)` should be
without the additional `/.` between `/dev/tty` and `usbmodem3d241`.
Also, open your console and go see if `ttyusbmodem3d241` exists. In the
console type `cd /dev` then `ls` and see if it is listed.
|
installing pybrain
Question: I am trying to install pybrain using :
git clone git://github.com/pybrain/pybrain.git
I installed git and then used windows command prompt to execute the above
command. Everything goes well but when I open my python IDE, I cant import
pybrain. The module doesn't exist. I wonder if I should've done something
extra.
Answer: As per the [PyBrain documentation](http://pybrain.org/docs/#installation),
you're missing a second step, which is to install the code. So open a command
prompt in the pybrain source directory (it'll have a `setup.py` file in it)
and then run the following command:
python setup.py install
For reference, more detailed installation instructions can be found at the
[PyBrain Github wiki](https://github.com/pybrain/pybrain/wiki/installation)
|
Pygame: Converting all white pixels to fully transparent in png image
Question: I have been trying to create an image processing program to take all the white
pixels (255,255,255) in a loaded image and set their alpha channels to 0 (non-
opaque), and then save the image.
I've been using Python's pygame extension to help me achieve this, but so far
I cannot find a simple way to do what I just described above.
Keep in mind I'm not trying to display an image, I'm trying to manipulate it.
Answer: I also suggest using PIL or
[ImageMagick](http://imagemagick.org/script/index.php "ImageMagick"), but here
is a way to do it in pygame:
import pygame
def convert():
pygame.init()
pygame.display.set_mode()
image = pygame.image.load("triangle.png").convert_alpha()
for x in range(image.get_width()):
for y in range(image.get_height()):
if image.get_at((x, y)) == (255, 255, 255, 255):
image.set_at((x, y), (255, 255, 255, 0))
pygame.image.save(image, "converted.png")
if __name__ == "__main__":
convert()
The above works for a white background. Here's how _triangle.png_ and
_converted.png_ look using magenta instead of white so you can see the
difference:
 
With the ImageMagick utility instead, it's as easy as running this on the
command line:
convert original.png -transparent white converted.png
|
python: I want to find the first record in google place result but getting first character
Question: I'm using google place API to return a list of locations. I would like to find
the first name from the result set. I'm getting a list of values, but when I
try to get just the first name, it gives me the first character instead.
name2 = simplejson.dumps([s['name'] for s in result['results']], indent=0)[0]
Obviously, there has to be a better way to get what I want, but I haven't
found it. Seems like I'm missing something pretty basic. Following is the
whole function:
import simplejson, urllib
PLACE_SEARCH = 'https://maps.googleapis.com/maps/api/place/textsearch/json'
def placelatlng(name,city, state, sensor,**geo_args):
geo_args.update({
'name': name,
'city': city,
'state': state,
'sensor': sensor
})
concat=name+'+'+city+'+'+state
query = {"query": concat }
key="MyKey"
url = PLACE_SEARCH + '?' + urllib.unquote(urllib.urlencode(query))+ '&' + "sensor="+sensor +'&' + "key="+key
result = simplejson.load(urllib.urlopen(url))
name2 = simplejson.dumps([s['name'] for s in result['results']], indent=0)
Thanks.
Answer: dumps() returns a string. `[0]` gets the first character in it.
To get the first result's name:
print result['results'][0]['name']
|
what "self" is doing in the selenium python code?
Question: > **Possible Duplicate:**
> [Python ‘self’
> explained](http://stackoverflow.com/questions/2709821/python-self-explained)
I just wrote a code as below with the help of `selenium` documentation, but
confused with one what `self` does some methods `argument list`? Why I need to
import `unittest` class?
import unittest
from selenium import webdriver
from selenium.webdriver.common.keys import Keys
class PythonOrgSearch(unittest.TestCase):
def setUp(self):
self.driver = webdriver.Firefox()
def test_search_in_python_org(self):
driver = self.driver
driver.get("http://www.python.org")
self.assertIn("Python", driver.title)
elem = driver.find_element_by_name("q")
elem.send_keys("selenium")
elem.send_keys(Keys.RETURN)
self.assertIn("Google", driver.title)
def tearDown(self):
self.driver.close()
if __name__ == "__main__":
unittest.main()
Answer: `self` is used to represent the calling instance of a class in case of member
methods. This is required so that the member methods of a class act on the
correct object. This does not have anything to do with Selenium, but is a
general feature of the language.
It is similar to the `this` argument in C++
When a class is defined, the `self` argument is used when defining data
members of the class as is being done in your class.
|
Viewing html text between tags (python, lxml, urllib, xpath)
Question: I am trying to parse some html and I want to retrieve the actual html between
the tags, but instead my code is giving me what I believe is the location of
the elements.
Here is my code so far:
import urllib.request, http.cookiejar
from lxml import etree
import io
site = "http://somewebsite.com"
cj = http.cookiejar.CookieJar()
request = urllib.request.Request(site)
opener = urllib.request.build_opener(urllib.request.HTTPCookieProcessor(cj))
request.add_header('User-agent', 'Mozilla/5.0 (Windows NT 6.1; WOW64; rv:17.0) Gecko/20100101 Firefox/17.0')
html = etree.HTML(opener.open(request).read())
xpath = "//li[1]//cite[1]"
filtered_html = html.xpath(xpath)
print(filtered_html)
Here is a piece of the html:
<div class="f kv">
<cite>
www.
<b>hello</b>
online.com/
</cite>
<span class="vshid">
</div>
Currently my code returns:
[<Element cite at 0x36a65e8>, <Element cite at 0x36a6510>, <Element cite at 0x36a64c8>]
How do I extract the actual html code between the cite tags? If I add
"/text()" to the end of my xpath it gets me closer, but it leaves out what is
in the b tags. My ultimate goal is for my code to give me
"www.helloonline.com/".
Thank you
Answer: Use `//text()` to get _all_ text elements from a given location:
text = filtered_html.xpath('//text()')
print ''.join(t.strip() for t in text) # prints "www.helloonline.com/"
|
How do I use python's choice just once?
Question: Consider the following:
I'm making a secret santa script for my family for next year using python, and
although I have figured out how to draw names (see code below), I need to
execute it just once. I'm planning to use the flask framework to create a page
counts down the days until the draw (which I've figured out as well), but how
do i make it so it does the draw, just once, and not everytime somebody logs
on to that page? Get what I mean?
Anyway, I'll show you my code here:
# imports & initial Flask set up above
def do_matchup(names, draw, matches=None):
if matches is None:
matches = []
while names:
member = names.pop()
recipient = choice(draw)
if recipient != member:
matches.append("%s=%s" % (member, recipient))
draw.remove(recipient)
else:
names.append(member)
return matches
@app.route("/")
def index():
now = dt.datetime.now()
draw_date = dt.datetime.strptime('10/1/2013', '%m/%d/%Y')
days = draw_date - now
family = ["member1", "member2", "member3", "member4", "member5", "Me"]
hat_names = [name for name in family]
matchup = do_matchup(family, hat_names)
return render_template("base.html", now=now,
draw_date=draw_date,
days=days,
matchup=matchup)
The template is a basic html page that says {% if now < draw_date %} "There
are x-amount of days until the draw", {% else %} "Show the draw results".
Every time the page is loaded, it does a new draw. How do I make it so it just
does the draw once and not give every family member different results?
Answer: If you are not using a database and just need this small amount of saved
results, you could just pickle the matchup to a file. Then in your index you
just check if the file exists and if so, read the file and return that
matchup. Otherwise you generate a new matchup, save it, and return results.
|
Python Spacing Between Print Calls
Question: I would like to make the spacing between print statements the same. I thought
that the spacing would be the same but between the third and fourth lines of
text there is a larger gap.
Here is my code
import random
import time
def UserInfo():
UserName = input ("Player 1 what is your name?\n")
return UserName
def Introduction(UserName):
time.sleep(.5)
print ("Hello " + UserName + ",\n")
time.sleep(1)
print ("You are an unfortunate soul\n")
UserName = UserInfo()
Introduction(UserName)
The result i am getting is
Player 1 what is your name?
Patrick
Hello Patrick,
You are an unfortunate soul
But I dont want the gap between the third and fourth lines
Answer: If you don't want extra linebreaks, don't use extra `\n`s. `print` adds a line
feed by default.
|
threading python bind several ports
Question: I want to do a simple thing: just bind two ports to wait for incoming
connections and continous with the application code. This is the code.
import socket
import threading
import Queue
q = Queue.Queue()
q2 = Queue.Queue()
def escucha_9003():
s = socket.socket()
s.bind(("localhost",9023))
s.listen(10)
sc, address = s.accept()
q.put(sc)
def escucha_9004():
s2 = socket.socket()
s2.bind(("localhost",9024))
s2.listen(10)
sc2, address2 = s2.accept()
q.put(sc2)
hilo = threading.Thread(target=escucha_9003).start()
sc2=q.get()
hilo2 = threading.Thread(target=escucha_9004).start()
sc=q2.get()
print "i never arrive here"
I need to get some parameters that are returned in each function. I use Queue
library to do it. But the problem is that i want to keep working with the code
and I never arrive to the line: print "i never arrive here". At least it is
never printed.
How need I do it to continue developing after launch those two threads and
work with the incoming connections.
Thank you very much
Answer: Both `.get()` calls are blocking calls. Also, the `.accept()` calls in your
threads are blocking. Technically you should never even get past the two
`.accept()` calls if no connections are coming in from clients. Because the
main thread is waiting on `get()` calls from the queues, but the queues never
put anything because the threads are waiting on accepting a future connection.
What you would need to do is handle your queues from within threads instead of
inside of the main thread. Otherwise, you will need to use
`.get(timeout=someSeconds)` inside of an event loop where you keep checking
for more stuff in your queues for a certain amount of time, and then move on
to do more continuous processing.
You may want to explain exactly what you are trying to achieve, and then
restructure these threads to handle a bit more of their own work before
blocking the main thread to receive data.
|
list inteprolation removing arbitary values - np.interp
Question: I am new to python coding:
I have a list of temperatures, for days where temperature was not recorded the
value 9999 is used. I want to use np.interp tp interpolate through the list to
remove 9999, with an estimated value. E.g.
max_temp = [40, 35, 32, 31, 9999, 9999, 9999, 26, 27, ... ... 40, 42]
Answer: Solved - Used:
from pandas import *
a = [1,2,3,None,5]
b = Series(a).interpolate()
b = [1,2,3,4,5]
Simpler than np.interp()
|
Python SSL Socket Client Authentification
Question: I'm trying to set up a server and client in python where the server
authenticates clients using SSL with certificates. There are a lot of examples
of SSL certificates online, but everything I've found has the server providing
a certificate to the client and the client checking it. I need the server to
ensure that the client has the authority to connect to the server. I
understand how to generate and send certificates and the basics of how they
work. I would type out my code, but my client/server without SSL is working
fine and I've been referencing
[this](http://docs.python.org/2/library/ssl.html) for SSL. The client/server
example at the bottom of that page summarizes my understanding of SSL certs in
python.
I realize this isn't much to go on, but if someone could explain the basic
modifications to that example to have the server authenticate the client
instead of the other way around, that would be awesome. Alternatively, a link
to an example or even just some socket methods to investigate would be very
helpful. Let me know if more information is needed. I don't mean to be vague
and promise I've spent all morning looking for info myself :).
Edit: I'm trying to stick to the basic ssl library. Aka "import ssl".
Answer: You would use
[SSLSocket.getpeercert](http://docs.python.org/2/library/ssl.html#ssl.SSLSocket.getpeercert)
to get the certificate. The client would need to specify a key and certificate
when wrapping the socket just like the server side. On the server side, you
will also need to pass ca_certs="path_to_ca_cert_file" and probably also want
to specify cert_reqs=CERT_REQUIRED (see. args for
[ssl.wrap_socket](http://docs.python.org/2/library/ssl.html#ssl.wrap_socket).
In addition to this, it sounds like you might be looking to do certificate
based client authentication/authorization? This is a simple matter of using
getpeercert to get the client certificate and accessing fields within the
certificate to use in a normal authentication path (i.e. Common Name == User
Id)
|
Equivalent to: import *
Question: I am creating a Perl equivalent to my Python project.
Description: I have a base module "base.py" that is used by all my scripts via
"from base import *" The base module has common subroutines/functions that can
be executed inside the scripts
My attempt for Perl was placing inside each script "use base.pm". However the
subroutines in Perl were not locally imported to the script so I needed to
make a call to the "base" module each time I wanted to execute a subroutine.
What is the Perl equivalent to Python's "from base import *"?
Answer: You generally specify which functions to import just as a list of names:
use List::Util 'max', 'min';
Most modules that export things will follow these semantics:
use MyBase; # imports default exports (if any)
use MyBase 'baz'; # imports only baz
use MyBase (); # import nothing
Inside the module, an import class method is called that can choose what to
export, usually having a default list but using the list passed if there is
one. The Exporter module exists to help you do this:
package MyBase;
use Exporter 'import';
our @EXPORT = ( 'foo', 'bar' );
our @EXPORT_OK = ( 'baz', 'quux' );
There is also a facility for grouping exports by tag and allowing importing a
whole group easily, see the Exporter docs. Variables can also be exported, not
just subs.
With that background, to finally answer your question:
For modules that use Exporter (not all do), you can specify imports with a
regular expression enclosed in //:
use List::Util '/./';
|
Python, subprocess, call(), check_call and returncode to find if a command exists
Question: I've figured out how to use call() to get my python script to run a command:
import subprocess
mycommandline = ['lumberjack', '-sleep all night', '-work all day']
subprocess.call(mycommandline)
This works but there's a problem, what if users don't have lumberjack in their
command path? It would work if lumberjack was put in the same directory as the
python script, but how does the script know it should look for lumberjack? I
figured if there was a command-not-found error then lumberjack wouldn't be in
the command path, the script could try to figure out what its directory is and
look for lumberjack there and finally warn the user to copy lumberjack into
one of those two places if it wasn't found in either one. How do I find out
what the error message is? I read that check_call() can return an error
message and something about a returncode attribute. I couldn't find examples
on how to use check_call() and returncode, what the message would be or how I
could tell if the message is command-not-found.
Am I even going about this the right way?
Answer: A simple snippet:
try:
subprocess.check_call(['executable'])
except subprocess.CalledProcessError:
pass # handle errors in the called executable
except OSError:
pass # executable not found
|
Could not import settings in zc.buildout
Question: I just setup my project and I'm having a problem getting Django to work.
Here's my `buildout.cfg`:
[buildout]
parts = python django
develop = .
eggs = myproject
[python]
recipe = zc.recipe.egg
interpreter = python
eggs = ${buildout:eggs}
[django]
recipe = djangorecipe
project = myproject
settings = settings
wsgi = true
fcgi = true
I generated my Django project by running
$ bin/django startproject myproject src/
The settings file definitely exists and looks fine, but I get the following
error:
> Error: Could not import settings 'myproject.settings' (Is it on sys.path?):
> No module named myproject.settings
Any ideas as to what's going wrong?
Answer: You haven't told your `[django]` part which eggs to use.
You normally have two or three parts in a buildout where you need the very
same eggs. In your case the `[django]` and `[python]` part. Best practice is
to add an `eggs` option to `[buildout]` (as you've done) and to use that in
the other relevant parts as `eggs = ${buildout:eggs}`.
So... you're only missing that line in your `[django]` part.
|
How to download images from a list of scraped URLs?
Question: > **Possible Duplicate:**
> [How to download image using
> requests](http://stackoverflow.com/questions/13137817/how-to-download-image-
> using-requests)
I have this Python script for scraping image URLs of a tumblr blog, and would
like to download them to a local folder on my desktop. How would I go about
implementing this
import requests
from bs4 import BeautifulSoup
def make_soup(url):
#downloads a page with requests and creates a beautifulsoup object
raw_page = requests.get(url).text
soup = BeautifulSoup(raw_page)
return soup
def get_images(soup):
#pulls images from the current page
images = []
foundimages = soup.find_all('img')
for image in foundimages:
url = img['src']
if 'media.tumblr.com' in url:
images.append(url)
return images
def scrape_blog(url):
# scrapes the entire blog
soup = make_soup(url)
next_page = soup.find('a' id = 'nextpage')
while next_page is not none:
soup = make_soup(url + next_page['href'])
next_page = soup.find('a' id = 'nextpage')
more_images = get_images(soup)
images.extend(more_images)
return images
url = 'http://x.tumblr.com'
images = scrape_blog(url)
Answer: Python's "[urllib2](http://docs.python.org/2/howto/urllib2.html)" is probably
what you're looking for. If you need to do anything complicated (such as with
cookies or authentication) it may be worth looking into a wrapper library such
as [Requests](https://github.com/kennethreitz/requests), which provides a nice
wrapper around a lot of the more cumbersome features of the standard library.
|
Set a cookie and retrieve it with Python and WSGI
Question: a lot of questions exists that are similar to this, but none of them helped me
out. Basically I'm using WSGI start_response() method
[link](http://www.python.org/dev/peps/pep-0333/#the-start-response-callable).
I tried to set a dummy header in the response with the tuple [('Set-Cookie',
'token=THE_TOKEN')] and add it to start response like this:
status = '200 OK'
response = 'Success'
start_response(status,[('Set-Cookie', "DMR_TOKEN=DMR_TOKEN")])
return response
I'm not pretty sure that is working correctly, but it's here [setting
cookies](http://pylonsbook.com/en/1.1/the-web-server-gateway-interface-
wsgi.html#changing-the-status-and-headers). Now, let's suppose the header is
correct and in following requests I want to authenticate a token. What would
be the correct way to catch that cookie/header setted in the past ?
I've been reading and find I need something like this:
(environ.get("HTTP_COOKIE",""))
but that has been yielding empty string all the time, so I'm just assuming the
header/cookie is not correctly set.
Thanks guys
Answer: I think you need to set the path explicitly to get useful behavior out of
cookies, try something like:...
from Cookie import SimpleCookie
def my_app(environ, start_response):
session_cookie = SimpleCookie()
session_cookie['session'] = "somedata"
session_cookie['session']["Path"] = '/'
headers = []
headers.extend(("set-cookie", morsel.OutputString())
for morsel
in session_cookie.values())
start_response("200 OK", headers)
|
Issue while importing nltk package in Python
Question: When I type
import nltk
in the Python interpreter, it gives me this --
>>> import nltk
Traceback (most recent call last):
File "<stdin>", line 1, in <module>
File "/usr/local/lib/python2.7/dist-packages/nltk/__init__.py", line 105, in <module>
from collocations import *
File "/usr/local/lib/python2.7/dist-packages/nltk/collocations.py", line 38, in <module>
from nltk.metrics import ContingencyMeasures, BigramAssocMeasures, TrigramAssocMeasures
File "/usr/local/lib/python2.7/dist-packages/nltk/metrics/__init__.py", line 16, in <module>
from nltk.metrics.scores import (accuracy, precision, recall, f_measure,
File "/usr/local/lib/python2.7/dist-packages/nltk/metrics/scores.py", line 16, in <module>
from scipy.stats.stats import betai
File "/usr/lib/python2.7/dist-packages/scipy/stats/__init__.py", line 7, in <module>
from stats import *
File "/usr/lib/python2.7/dist-packages/scipy/stats/stats.py", line 198, in <module>
import distributions
File "/usr/lib/python2.7/dist-packages/scipy/stats/distributions.py", line 87, in <module>
from new import instancemethod
File "new.py", line 3
^
IndentationError: expected an indented block
I took a look at new.py which I found in /usr/lib/python2.7/ and found
everything ok.
"""Create new objects of various types.
Deprecated.This module is no longer required except for backward compatibility.
Objects of most types can now be created by calling the type object.
"""
from warnings import warnpy3k
warnpy3k("The 'new' module has been removed in Python 3.0; use the 'types' "
"module instead.", stacklevel=2)
del warnpy3k
from types import ClassType as classobj
from types import FunctionType as function
from types import InstanceType as instance
from types import MethodType as instancemethod
from types import ModuleType as module
from types import CodeType as code
Any solutions?
Answer: You have a _local_ file named `new.py`. Check your current directory and
rename it or delete it.
You can see this in the traceback:
File "/usr/lib/python2.7/dist-packages/scipy/stats/distributions.py", line 87, in <module>
from new import instancemethod
File "new.py", line 3
The preceding module has a full filepath, but the `new.py` file does not,
making it a local file that is shadowing the relative import in
`scipy.stats.distributions`.
|
Processing data after returning content - GAE Python
Question: I want to collect some statistical data which needs some time to process, but
it is not going affect user content which is returning. I am currently doing
it by first caching, then processing it with a cron job.
Is there any way to do this job immediately after returning user content?
It should be like:
def post(self):
self.response.out.write("some output")
# here user should not wait any more output
# loading should be end in user browser.
collectSomeStatistics(self)
(I am using Python 2.7)
Answer: You can use the [deferred
library](https://developers.google.com/appengine/articles/deferred)
from google.appengine.ext import deferred
def do_something_expensive(a, b, c=None):
logging.info("Doing something expensive!")
# Do your work here
# Somewhere else
deferred.defer(do_something_expensive, "Hello, world!", 42, c=True)
So your code becomes:
def post(self):
deferred.defer(collectSomeStatistics,args)
self.response.out.write("some output")
This then executes your function as a separate task, and the call to deferred
returns immediately. Of course you won't be able to include any results from
that deferred function in the content you return to the user.
|
Convert a string to a whitespace separated list w/quoted elements
Question: Is there a simple way in Python to convert a string to a list using
whitespaces as separators, but ignoring the whitespace within quoted text? IE:
each word is treated as a separate search term, but any quoted text is treated
as one term.
Answer: Yes, by using the [`shlex.split()`
function](http://docs.python.org/2/library/shlex.html#shlex.split):
>>> import shlex
>>> shlex.split('Some whitespace "separated string"')
['Some', 'whitespace', 'separated string']
|
Ensure two Pandas DatetimeIndexes are the same?
Question: I have run into an issue when comparing two `DatetimeIndex`'s with different
lengths in an `assert` like the following:
In [1]: idx1 = pd.date_range('2010-01-01','2010-12-31',freq='D')
In [2]: idx2 = pd.date_range('2010-01-01','2010-11-01',freq='D')
In [3]: assert (idx1 == idx2).all()
I get the error:
---------------------------------------------------------------------------
AttributeError Traceback (most recent call last)
<ipython-input-17-ad2cfd6d11c2> in <module>()
----> 1 assert (idx1 == idx2).all()
/opt/local/Library/Frameworks/Python.framework/Versions/2.7/lib/python2.7/site-packages/pandas-0.10.1.dev_dcd9df7-py2.7-macosx-10.8-x86_64.egg/pandas/tseries/index.pyc in wrapper(self, other)
75 result = func(other)
76
---> 77 return result.view(np.ndarray)
78
79 return wrapper
AttributeError: 'NotImplementedType' object has no attribute 'view'
Which is fine if this is not implemented, yet, but is there some **pandas**
way of doing this?
**Note:** I have used the following with success:
In [3]: assert list(idx1) == list(idx2)
So, the following also works:
In [3]: assert list(df.index) == list(testindex)
But I would like to know if there is a more `pandas`-ish way of doing this.
Answer:
In [1]: import pandas as pd
In [2]: idx1 = pd.date_range('2010-01-01','2010-12-31',freq='D')
In [3]: idx2 = pd.date_range('2010-01-01','2010-11-01',freq='D')
In [4]: idx3 = pd.date_range('2010-01-01','2010-12-31',freq='D')
In [5]: help(idx1.equals)
Help on method equals in module pandas.tseries.index:
equals(self, other) method of pandas.tseries.index.DatetimeIndex instance
Determines if two Index objects contain the same elements.
In [6]: print(idx1.equals(idx2))
False
In [7]: print(idx1.equals(idx3))
True
|
Pygame installation for Python 3.3
Question: I am trying to import [Pygame](https://en.wikipedia.org/wiki/Pygame) to use
for my version of
[Python](http://en.wikipedia.org/wiki/Python_%28programming_language%29), 3.3.
The downloads on the Pygame website only have Python 3.1 and 3.2. I cannot
seem to be able to import Pygame though I thought I had it installed in the
correct path. I have tried both the 3.1 and 3.2 Pygame downloads.
Is Pygame just not installed in the correct file path or is Pygame not
compatible with my version of Python (3.3)?
I am running Windows 7 and here is the error:
Traceback (most recent call last):
File "<pyshell#3>", line 1, in <module>
import pygame
File ".\pygame\__init__.py", line 95, in <module>
from pygame.base import *
ImportError: DLL load failed: The specified module could not be found.
Answer: The main Pygame page seems to be rarely updated. You can download Pygame
releases direct from [Bitbucket](http://en.wikipedia.org/wiki/Bitbucket) at
<https://bitbucket.org/pygame/pygame/downloads>.
|
Boost::python wrapper for derived class method
Question: I have C++ class and its wrapper for boost::python:
class CApp
{
public:
virtual bool FOOs (){}; //does not matter for now
bool Run( const char * First,const char * Last)
{
...
return "Running..."
};
struct pyApp : CApp, wrapper<CApp> //derived class
{
... // wrappers for virtual methods
}
#include <boost/python.hpp>
using namespace boost::python;
BOOST_PYTHON_MODULE( myApp )
{
class_<pyApp, boost::noncopyable>("CApp", init<>() )
...
.def("Run",&pyMOOSApp::Run);
}
Compiling is OK. But when i'm invoking Python code
from myApp import *
class pyApp(CApp):
def __init__(self):
print "INIT-->"
CClass = CApp()
pyClass = pyApp()
CClass.Run('myApp','bar')
pyClass.Run('myApp','bar')
I have an error:
INIT-->
Running... // this is from CClass.Run
Traceback (most recent call last):
File "./pytest.py", line 18, in <module>
pyClass.Run('myApp','bar')
Boost.Python.ArgumentError: Python argument types in
CApp.Run(pyApp, str, str)
did not match C++ signature:
Run(CApp {lvalue}, char const*, char const*)
So I've tries to write a wrapper for Run method that is converting str to char
placed in derived class c++ code:
bool Run(std::string a, std::string b) {
char * cstrA;
char * cstrB;
cstrA = new char[a.size()+1];
cstrB = new char[b.size()+1];
strcpy(cstrA,a.c_str());
strcpy(cstrB,b.c_str());
return this -> CApp::Run(cstrA, cstrB);
}
But the only change was in the last stroke:
did not match C++ signature:
Run(pyApp {lvalue}, std::string, std::string)
**I'm pretty sure that a have bad wrapper for the Run method** , so any help
will be appreciated. Thank you.
Answer: I just saw your other question ([Using derived class (C++) by Python
BOOST](http://stackoverflow.com/q/14076708/82896)) and believe this has the
same solution. You need to call init() on the base class if you provide an
init in the derived class. See my solution here -
<http://stackoverflow.com/a/14742937/82896>.
|
gui locked when calling QWebView.print_()
Question: I'm working with **Python 2.7** and **PySide** , and i need to export a big
html-file to a pdf-file.
I have tried loading it with a `QWebView` and then printing it to a `QPrinter`
configured for pdf-format. this works fine.
However, there is one big problem with my solution: when I call
`QWebView.print_()`, the gui is locked up, and for windows it looks like my
program has crashed. This happens because of the big size of my html (1000
pages and more).
So my question is: is there a clean way to avoid this 'crash' ?
EDIT:
I tried to do the printing in a separate thread, like jadkik94 suggested. As
far as I understand the code below should work. Unfortunately it crashes
randomly. ;) Any ideas why this is the case?
import sys
from PySide import QtGui, QtWebKit, QtCore
class PrintThread(QtCore.QThread):
def __init__(self, webview, printer, parent=None):
super(PrintThread, self).__init__(parent)
self._webview = webview
self._printer = printer
def run(self):
self._webview.print_(self._printer)
class MyWindow(QtGui.QMainWindow):
def __init__(self):
super(MyWindow,self).__init__()
# a printer to print on
self._myPrinter = QtGui.QPrinter()
self._myPrinter.setOutputFormat(QtGui.QPrinter.PdfFormat)
self._myPrinter.setPrintRange(QtGui.QPrinter.AllPages)
self._myPrinter.setOrientation(QtGui.QPrinter.Portrait)
self._myPrinter.setPaperSize(QtGui.QPrinter.A4)
self._myPrinter.setNumCopies(1)
# a webview for loading the html and printing it
self._webview = QtWebKit.QWebView(self)
self.setCentralWidget( self._webview )
self._webview.loadFinished.connect(self.webViewLoadFinished)
# print-preview-dialog
self._previewDlg = QtGui.QPrintPreviewDialog(self._myPrinter)
#self._previewDlg.paintRequested.connect(self.dlgPaintRequestNoThread) # works but freezes the mainthread
self._previewDlg.paintRequested.connect(self.dlgPaintRequestWithThread) # as far is i understand this should work... but crashes randomly ;)
# load the html
self._webview.load('index.htm') # file is 2MB
def webViewLoadFinished(self):
# when webview has finished loading, show the dialog
self._previewDlg.show()
def dlgPaintRequestNoThread(self):
self._webview.print_(self._myPrinter)
def dlgPaintRequestWithThread(self):
self.printPages()
# wait for the print-thread to finish without blocking the mainthread
eventLoop = QtCore.QEventLoop()
self.worker.finished.connect(eventLoop.quit)
eventLoop.exec_()
def printPages(self):
self.worker = PrintThread(self._webview, self._myPrinter)
self.worker.finished.connect(self.donePrinting)
self.progressDlg = QtGui.QProgressDialog()
self.progressDlg.setCancelButton(None)
self.progressDlg.show()
self.worker.start()
def donePrinting(self):
self.progressDlg.close()
if __name__ == '__main__':
app = QtGui.QApplication(sys.argv)
window = MyWindow()
window.show()
app.exec_()
Answer: I believe you need to use threads to solve this problem. It appears that
`QWebView.print_()` runs in the main thread, and thus blocks your GUI from
running.
You have 2 options, you either use Python's `threading` module or Qt's
`QThread`s.
[This question](http://stackoverflow.com/questions/10044197/how-to-get-
qthreads-to-work-in-a-console-pyside-program) shows how you can use
`QThread`s. Basically:
class PrintThread(QtCore.QThread):
def __init__(self, webview, parent=None):
super(PrintThread, self).__init__(parent)
self.webview = webview
def run(self):
# Get a printer from somewhere
self.webview.print_(printer)
And then:
def printPage(self):
worker = PrintThread(self.page)
worker.finished.connect(self.donePrinting)
# Show a loading dialog
worker.start()
def donePrinting(self):
# Close the loading dialog
pass
You could apply the same thing with the threading module, but since you are
already using pyside, why not use it for that too. Also, I am not sure if
another thread (other than QThread) can mess with the Qt GUI, it might just
tell you you cannot access the GUI thread from another thread (not sure
though).
|
Python list comprehension expensive
Question: Im trying to find the effeciency of list comprehension but it look like its
more expensive than a normal function operation. Can someone explain?
def squares(values):
lst = []
for x in range(values):
lst.append(x*x)
return lst
def main():
t = timeit.Timer(stmt="lst = [x*x for x in range(10)]")
print t.timeit()
t = timeit.Timer(stmt="squares",setup="from __main__ import squares")
print t.timeit()
lst = [x*x for x in range(10)]
print lst
print squares(10)
----Output:---
2.4147507644
0.0284455255965
[0, 1, 4, 9, 16, 25, 36, 49, 64, 81]
[0, 1, 4, 9, 16, 25, 36, 49, 64, 81]
For the same output, the normal function calculates in very less time compared
to the list comprehension.
I thought the list comprehension is more effecient.
Answer: You are never _calling_ your `squares` function, so it is not doing anything.
List comprehensions _are_ in fact faster:
>>> import timeit
>>> def squares(values):
... lst = []
... for x in range(values):
... lst.append(x*x)
... return lst
...
>>> def squares_comp(values):
... return [x*x for x in range(values)]
...
>>> timeit.timeit('f(10)', 'from __main__ import squares as f')
3.9415171146392822
>>> timeit.timeit('f(10)', 'from __main__ import squares_comp as f')
2.3243820667266846
If you use the `dis` module to look at the bytecode for each function, you can
see why:
>>> import dis
>>> dis.dis(squares)
2 0 BUILD_LIST 0
3 STORE_FAST 1 (lst)
3 6 SETUP_LOOP 37 (to 46)
9 LOAD_GLOBAL 0 (range)
12 LOAD_FAST 0 (values)
15 CALL_FUNCTION 1
18 GET_ITER
>> 19 FOR_ITER 23 (to 45)
22 STORE_FAST 2 (x)
4 25 LOAD_FAST 1 (lst)
28 LOAD_ATTR 1 (append)
31 LOAD_FAST 2 (x)
34 LOAD_FAST 2 (x)
37 BINARY_MULTIPLY
38 CALL_FUNCTION 1
41 POP_TOP
42 JUMP_ABSOLUTE 19
>> 45 POP_BLOCK
5 >> 46 LOAD_FAST 1 (lst)
49 RETURN_VALUE
>>> dis.dis(squares_comp)
2 0 BUILD_LIST 0
3 LOAD_GLOBAL 0 (range)
6 LOAD_FAST 0 (values)
9 CALL_FUNCTION 1
12 GET_ITER
>> 13 FOR_ITER 16 (to 32)
16 STORE_FAST 1 (x)
19 LOAD_FAST 1 (x)
22 LOAD_FAST 1 (x)
25 BINARY_MULTIPLY
26 LIST_APPEND 2
29 JUMP_ABSOLUTE 13
>> 32 RETURN_VALUE
The `squares` function looks up the `.append()` method of the list in each
iteration, and calls it. The `.append()` function has to grow the list by one
element each time it is called.
The list comprehension on the other hand doesn't have to do that work.
Instead, python uses the `LIST_APPEND` bytecode, which uses the C API to
append a new element to the list, without having to do the lookup and a python
call to the function.
|
Two Columns of a pandas dataframe - Concat in Python
Question: New to pandas python.
I have a dataframe (df) with two columns of cusips. I want to turn those
columns into a list of the unique entries of the two columns.
My first attempt was to do the following:
cusips = pd.concat(df['long'], df['short']).
This returned the error: The truth value of an array with more than one
element is ambiguous. Use a.any() or a.all().
I have read a few postings, but I am still having trouble with why this comes
up. What am I missing here?
Also, what's the most efficient way to select the unique entries in a column
or a dataframe? Can I call it in one function? Does the function differ if I
want to create a list or a new, one-coulmn dataframe?
Thank you.
Answer: To obtain the unique values in a column you can use the
[`unique`](http://pandas.pydata.org/pandas-
docs/dev/generated/pandas.Series.unique.html#pandas.Series.unique) Series
method, which will return a numpy array of the unique values _(and it is
fast!)_.
df.long.unique()
# returns numpy array of unique values
You could then use
[`numpy.append`](http://docs.scipy.org/doc/numpy/reference/generated/numpy.append.html):
np.append(df.long.unique(), df.short.unique())
Note: This just appends the two unique results together and so itself is not
unique!
.
Here's a (trivial) example:
import pandas as pd
import numpy as np
df = pd.DataFrame([[1, 2], [1, 4]], columns=['long','short'])
In [4]: df
Out[4]:
long short
0 1 2
1 1 4
In [5]: df.long.unique()
Out[5]: array([1])
In [6]: df.short.unique()
Out[6]: array([2, 4])
And then [appending the resulting two
arrays](http://stackoverflow.com/a/9775378/1240268):
In [7]: np.append(df.long.unique(), df.short.unique())
Out[7]: array([1, 2, 4])
Using @Zalazny7's `set` is significantly faster (since it runs over the array
only once) and somewhat upsettingly it's even faster than
[`np.unique`](http://docs.scipy.org/doc/numpy/reference/generated/numpy.unique.html)
_(which sorts the resulting array!)_.
|
What do I import: file_name or class in Python?
Question: I have a file named **schedule.py** :
class SchedGen:
""" Class creates a pseudo random Schedule.
With 3/4 of total credit point required for graduation"""
def __init__(self, nof_courses=40):
random.seed()
self.courses = {}
self.nof_courses = nof_courses
for i in xrange(nof_courses):
self.courses[i] = college.Course(i)
self.set_rand_cred()
self.set_rand_chance()
self.set_rand_preq_courses()
def set_rand_cred(self):
""" Set random credit to courses uniformly between 2 and 6"""
temp_dict = self.courses.copy()
While importing content of schedule do I do `import schedule` like:
import schedule
If that's correct how can I access the function set_rand_cred(self) from
SchedGen class?
Answer: You can either do
import schedule
schedgen = schedule.SchedGen()
schedgen.set_rand_red()
or
from schedule import SchedGen
schedgen = SchedGen()
schedgen.set_rand_red()
This link provides some information how Pythons [import
statement](http://effbot.org/zone/import-confusion.htm) works.
|
Protocol error between Android and Python using SSL
Question: This question has been asked, in various flavors, several times.
Unfortunately, none of the answers have yielded a solution for me.
I am attempting to connect to a python web server (code to follow) using the
https protocol, with client side authentication included. When I connect via a
python client that I wrote for testing, I have no problems. Fast forward, I am
now trying to connect from an Android device (code to follow again) and am
getting a
javax.net.ssl.SSLProtocolException
I have a self signed CA, which has issued two certificates. One for the client
and one for the server.
I removed the passphrase from the server private key using:
`openssl rsa -in serverKey.pem -out serverKey.pem`
and issued a request using openssl from the linux command line.
For the client I issued a request, created the certificate and then used
keytool with the BouncyCastle provider to import the CA into a trust store and
the client certificate into a key store (I realize they are the same format,
it just helps me to keep them separated if I refer to them by different
names).
Relevant server code:
class ReuseHTTPServer(BaseHTTPServer.HTTPServer):
def __init__(self, address, handler):
BaseHTTPServer.HTTPServer.__init__(self, address, handler)
self.address = address
ssl_socket = ssl.wrap_socket(socket.socket(self.address_family,
self.socket_type),
keyfile = KEY_PATH,
certfile = CERTIFICATE_PATH,
server_side = True,
cert_reqs = ssl.CERT_REQUIRED,
ssl_version = ssl.PROTOCOL_SSLv23,
ca_certs = CA_PATH)
s = self.socket.getsockname()
print "serving:", s[0], "on port:", s[1]
self.socket = ssl_socket
self.server_bind()
self.server_activate()
def server_bind(self):
BaseHTTPServer.HTTPServer.server_bind(self)
Android client code:
//add bouncy castle to the list of security providers
Security.insertProviderAt(new BouncyCastleProvider(), 1);
//load the trusted CA
KeyStore trusted = KeyStore.getInstance("BKS");
InputStream in = getResources().openRawResource(R.raw.mobilecastore);
trusted.load(in, "password".toCharArray());
in.close();
TrustManagerFactory trust_factory = TrustManagerFactory.getInstance(TrustManagerFactory.getDefaultAlgorithm());
trust_factory.init(trusted);
//load the client keystore
KeyStore client = KeyStore.getInstance(KeyStore.getDefaultType());
InputStream client_in = getResources().openRawResource(R.raw.client);
client.load(client_in, "password2".toCharArray());
client_in.close();
KeyManagerFactory key_factory = KeyManagerFactory.getInstance(KeyManagerFactory.getDefaultAlgorithm());
key_factory.init(client, "password2".toCharArray());
SSLContext ssl_context = SSLContext.getInstance("SSL");
ssl_context.init(key_factory.getKeyManagers(), trust_factory.getTrustManagers(), null);
URL url = new URL("https", IP, 60000, "/cgi-bin/www_sel_jf");
connection = (HttpsURLConnection) url.openConnection();
connection.setSSLSocketFactory(ssl_context.getSocketFactory());
connection.setDoInput(true);
connection.setRequestMethod("GET");
connection.connect();
The error:
12-31 07:23:37.917: W/System.err(3666): javax.net.ssl.SSLHandshakeException: javax.net.ssl.SSLProtocolException: SSL handshake terminated: ssl=0x16bab18: Failure in SSL library, usually a protocol error
12-31 07:23:37.917: W/System.err(3666): error:14094410:SSL routines:SSL3_READ_BYTES:sslv3 alert handshake failure (external/openssl/ssl/s3_pkt.c:1234 0x16bf980:0x00000003)
12-31 07:23:37.917: W/System.err(3666): at org.apache.harmony.xnet.provider.jsse.OpenSSLSocketImpl.startHandshake(OpenSSLSocketImpl.java:460)
12-31 07:23:37.917: W/System.err(3666): at org.apache.harmony.xnet.provider.jsse.OpenSSLSocketImpl.startHandshake(OpenSSLSocketImpl.java:257)
12-31 07:23:37.917: W/System.err(3666): at libcore.net.http.HttpConnection.setupSecureSocket(HttpConnection.java:210)
12-31 07:23:37.917: W/System.err(3666): at libcore.net.http.HttpsURLConnectionImpl$HttpsEngine.makeSslConnection(HttpsURLConnectionImpl.java:477)
12-31 07:23:37.917: W/System.err(3666): at libcore.net.http.HttpsURLConnectionImpl$HttpsEngine.connect(HttpsURLConnectionImpl.java:441)
12-31 07:23:37.917: W/System.err(3666): at libcore.net.http.HttpEngine.sendSocketRequest(HttpEngine.java:282)
12-31 07:23:37.917: W/System.err(3666): at libcore.net.http.HttpEngine.sendRequest(HttpEngine.java:232)
12-31 07:23:37.917: W/System.err(3666): at libcore.net.http.HttpURLConnectionImpl.connect(HttpURLConnectionImpl.java:80)
12-31 07:23:37.917: W/System.err(3666): at libcore.net.http.HttpsURLConnectionImpl.connect(HttpsURLConnectionImpl.java:164)
12-31 07:23:37.917: W/System.err(3666): at com.dsndata.sds2mobile.status.activities.ServerJobs$RetrieveJobNames.doInBackground(ServerJobs.java:143)
12-31 07:23:37.917: W/System.err(3666): at com.dsndata.sds2mobile.status.activities.ServerJobs$RetrieveJobNames.doInBackground(ServerJobs.java:1)
12-31 07:23:37.917: W/System.err(3666): at android.os.AsyncTask$2.call(AsyncTask.java:264)
12-31 07:23:37.925: W/System.err(3666): at java.util.concurrent.FutureTask$Sync.innerRun(FutureTask.java:305)
12-31 07:23:37.925: W/System.err(3666): at java.util.concurrent.FutureTask.run(FutureTask.java:137)
12-31 07:23:37.925: W/System.err(3666): at java.util.concurrent.ThreadPoolExecutor.runWorker(ThreadPoolExecutor.java:1076)
12-31 07:23:37.925: W/System.err(3666): at java.util.concurrent.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:569)
12-31 07:23:37.925: W/System.err(3666): at java.lang.Thread.run(Thread.java:856)
12-31 07:23:37.925: W/System.err(3666): Caused by: javax.net.ssl.SSLProtocolException: SSL handshake terminated: ssl=0x16bab18: Failure in SSL library, usually a protocol error
12-31 07:23:37.925: W/System.err(3666): error:14094410:SSL routines:SSL3_READ_BYTES:sslv3 alert handshake failure (external/openssl/ssl/s3_pkt.c:1234 0x16bf980:0x00000003)
12-31 07:23:37.925: W/System.err(3666): at org.apache.harmony.xnet.provider.jsse.NativeCrypto.SSL_do_handshake(Native Method)
12-31 07:23:37.925: W/System.err(3666): at org.apache.harmony.xnet.provider.jsse.OpenSSLSocketImpl.startHandshake(OpenSSLSocketImpl.java:410)
12-31 07:23:37.925: W/System.err(3666): ... 16 more
12-31 07:23:37.925: W/System.err(3666): javax.net.ssl.SSLHandshakeException: javax.net.ssl.SSLProtocolException: SSL handshake terminated: ssl=0x16bab18: Failure in SSL library, usually a protocol error
12-31 07:23:37.925: W/System.err(3666): error:14094410:SSL routines:SSL3_READ_BYTES:sslv3 alert handshake failure (external/openssl/ssl/s3_pkt.c:1234 0x16bf980:0x00000003)
12-31 07:23:37.925: W/System.err(3666): at org.apache.harmony.xnet.provider.jsse.OpenSSLSocketImpl.startHandshake(OpenSSLSocketImpl.java:460)
12-31 07:23:37.925: W/System.err(3666): at org.apache.harmony.xnet.provider.jsse.OpenSSLSocketImpl.startHandshake(OpenSSLSocketImpl.java:257)
12-31 07:23:37.925: W/System.err(3666): at libcore.net.http.HttpConnection.setupSecureSocket(HttpConnection.java:210)
12-31 07:23:37.925: W/System.err(3666): at libcore.net.http.HttpsURLConnectionImpl$HttpsEngine.makeSslConnection(HttpsURLConnectionImpl.java:477)
12-31 07:23:37.925: W/System.err(3666): at libcore.net.http.HttpsURLConnectionImpl$HttpsEngine.connect(HttpsURLConnectionImpl.java:441)
12-31 07:23:37.925: W/System.err(3666): at libcore.net.http.HttpEngine.sendSocketRequest(HttpEngine.java:282)
12-31 07:23:37.925: W/System.err(3666): at libcore.net.http.HttpEngine.sendRequest(HttpEngine.java:232)
12-31 07:23:37.925: W/System.err(3666): at libcore.net.http.HttpURLConnectionImpl.connect(HttpURLConnectionImpl.java:80)
12-31 07:23:37.925: W/System.err(3666): at libcore.net.http.HttpsURLConnectionImpl.connect(HttpsURLConnectionImpl.java:164)
12-31 07:23:37.925: W/System.err(3666): at com.dsndata.sds2mobile.status.activities.ServerJobs$RetrieveJobNames.doInBackground(ServerJobs.java:143)
12-31 07:23:37.932: W/System.err(3666): at com.dsndata.sds2mobile.status.activities.ServerJobs$RetrieveJobNames.doInBackground(ServerJobs.java:1)
12-31 07:23:37.932: W/System.err(3666): at android.os.AsyncTask$2.call(AsyncTask.java:264)
12-31 07:23:37.932: W/System.err(3666): at java.util.concurrent.FutureTask$Sync.innerRun(FutureTask.java:305)
12-31 07:23:37.932: W/System.err(3666): at java.util.concurrent.FutureTask.run(FutureTask.java:137)
12-31 07:23:37.932: W/System.err(3666): at java.util.concurrent.ThreadPoolExecutor.runWorker(ThreadPoolExecutor.java:1076)
12-31 07:23:37.932: W/System.err(3666): at java.util.concurrent.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:569)
12-31 07:23:37.932: W/System.err(3666): at java.lang.Thread.run(Thread.java:856)
12-31 07:23:37.932: W/System.err(3666): Caused by: javax.net.ssl.SSLProtocolException: SSL handshake terminated: ssl=0x16bab18: Failure in SSL library, usually a protocol error
12-31 07:23:37.932: W/System.err(3666): error:14094410:SSL routines:SSL3_READ_BYTES:sslv3 alert handshake failure (external/openssl/ssl/s3_pkt.c:1234 0x16bf980:0x00000003)
12-31 07:23:37.932: W/System.err(3666): at org.apache.harmony.xnet.provider.jsse.NativeCrypto.SSL_do_handshake(Native Method)
12-31 07:23:37.932: W/System.err(3666): at org.apache.harmony.xnet.provider.jsse.OpenSSLSocketImpl.startHandshake(OpenSSLSocketImpl.java:410)
12-31 07:23:37.932: W/System.err(3666): ... 16 more
It should be noted that I am using the javax.net.ssl library and not the
apache one.
EDIT: The python server is hosted on a Windows machine. Is there any extra
configuration that needs to be taken into account for ssl on a Windows port?
EDIT: Yes, there is something that needs to be done to allow SSL on a windows
port. Switched to port 443 (designated for SSL traffic) and am making (slow)
progress.
EDIT: I am now able to track the request using Wireshark (I am learning a lot
for this problem!) and Wireshark is telling me that there is a 405 error.
Which in SSL means that the certificate format is not recognized. The python
server is using PEM certificates (the only format allowed according to python
docs) and the certificates imported into the keystore on the Android device
are DER (to my knowledge the only format accepted by BKS).
Any help would be greatly appreciated.
Answer: This can be a SSL/TLS version or algorithms mismatch error. Your server uses
SSL v.2-3, while this is quite old and TLS 1.0-1.2 should be used. The best
way to debug this is to run Wireshark, and see which client and server's
SSL/TLS handshake packets are sent and when connection is dropped.
|
Killing child process when parent crashes in python
Question: I am trying to write a python program to test a server written in C. The
python program launches the compiled server using the `subprocess` module:
pid = subprocess.Popen(args.server_file_path).pid
This works fine, however if the python program terminates unexpectedly due to
an error, the spawned process is left running. I need a way to ensure that if
the python program exits unexpectedly, the server process is killed as well.
Some more details:
* Linux or OSX operating systems only
* Server code can not be modified in any way
Answer: I would [`atexit.register`](http://docs.python.org/2/library/atexit.html) a
function to terminate the process:
import atexit
process = subprocess.Popen(args.server_file_path)
atexit.register(process.terminate)
pid = process.pid
Or maybe:
import atexit
process = subprocess.Popen(args.server_file_path)
@atexit.register
def kill_process():
try:
process.terminate()
except OSError:
pass #ignore the error. The OSError doesn't seem to be documented(?)
#as such, it *might* be better to process.poll() and check for
#`None` (meaning the process is still running), but that
#introduces a race condition. I'm not sure which is better,
#hopefully someone that knows more about this than I do can
#comment.
pid = process.pid
* * *
Note that this doesn't help you if you do something nasty to cause python to
die in a non-graceful way (e.g. via `os._exit` or if you cause a
`SegmentationFault` or `BusError`)
|
Creating a hook to a frequently accessed object
Question: I have an application which relies heavily on a `Context` instance that serves
as the access point to the context in which a given calculation is performed.
If I want to provide access to the `Context` instance, I can:
1. rely on `global`
2. pass the `Context` as a parameter to all the functions that require it
I would rather not use `global` variables, and passing the `Context` instance
to all the functions is cumbersome and verbose.
How would you "hide, but make accessible" the calculation `Context`?
For example, imagine that `Context` simply computes the state (position and
velocity) of planets according to different data.
class Context(object):
def state(self, planet, epoch):
"""base class --- suppose `state` is meant
to return a tuple of vectors."""
raise NotImplementedError("provide an implementation!")
class DE405Context(Context):
"""Concrete context using DE405 planetary ephemeris"""
def state(self, planet, epoch):
"""suppose that de405 reader exists and can provide
the required (position, velocity) tuple."""
return de405reader(planet, epoch)
def angular_momentum(planet, epoch, context):
"""suppose we care about the angular momentum of the planet,
and that `cross` exists"""
r, v = context.state(planet, epoch)
return cross(r, v)
# a second alternative, a "Calculator" class that contains the context
class Calculator(object):
def __init__(self, context):
self._ctx = context
def angular_momentum(self, planet, epoch):
r, v = self._ctx.state(planet, epoch)
return cross(r, v)
# use as follows:
my_context = DE405Context()
now = now() # assume this function returns an epoch
# first case:
print angular_momentum("Saturn", now, my_context)
# second case:
calculator = Calculator(my_context)
print calculator.angular_momentum("Saturn", now)
Of course, I could add all the operations directly into "Context", but it does
not feel right.
In real life, the `Context` not only computes positions of planets! It
computes many more things, and it serves as the access point to a lot of data.
So, to make my question more succinct: how do you deal with objects which need
to be accessed by many classes?
I am currently exploring: python's context manager, but without much luck. I
also thought about dynamically adding a property "context" to all functions
directly (functions are objects, so they can have an access point to arbitrary
objects), i.e.:
def angular_momentum(self, planet, epoch):
r, v = angular_momentum.ctx.state(planet, epoch)
return cross(r, v)
# somewhere before calling anything...
import angular_momentum
angular_momentum.ctx = my_context
## edit
Something that would be great, is to create a "calculation context" with a
`with` statement, for example:
with my_context:
h = angular_momentum("Earth", now)
Of course, I can already do that if I simply write:
with my_context as ctx:
h = angular_momentum("Earth", now, ctx) # first implementation above
Maybe a variation of this with the [Strategy
pattern](http://en.wikipedia.org/wiki/Strategy_pattern)?
Answer: You generally don't want to "hide" anything in Python. You may want to signal
human readers that they should treat it as "private", but this really just
means "you should be able to understand my API even if you ignore this
object", not "you can't access this".
The idiomatic way to do that in Python is to prefix it with an underscore—and,
if your module might ever be used with `from foo import *`, add an explicit
`__all__` global that lists all the public exports. Again, neither of these
will actually prevent anyone from seeing your variable, or even accessing it
from outside after `import foo`.
See [PEP 8](http://www.python.org/dev/peps/pep-0008/#global-variable-names) on
Global Variable Names for more details.
Some style guides suggest special prefixes, all-caps-names, or other special
distinguishing marks for globals, but PEP 8 specifically says that the
conventions are the same, except for the `__all__` and/or leading underscore.
Meanwhile, the behavior you want is clearly that of a global variable—a single
object that everyone implicitly shares and references. Trying to disguise it
as anything other than what it is will do you no good, except possibly for
passing a `lint` check or a code review that you shouldn't have passed. All of
the problems with global variables come from being a single object that
everyone implicitly shares and references, not from being directly in the
`globals()` dictionary or anything like that, so any decent fake global is
just as bad as a real global. If that truly is the behavior you want, make it
a global variable.
Putting it together:
# do not include _context here
__all__ = ['Context', 'DE405Context', 'Calculator', …
_context = Context()
Also, of course, you may want to call it something like `_global_context` or
even `_private_global_context`, instead of just `_context`.
But keep in mind that globals are still members of a module, not of the entire
universe, so even a public `context` will still be scoped as `foo.context`
when client code does an `import foo`. And this may be exactly what you want.
If you want a way for client scripts to import your module and then control
its behavior, maybe `foo.context = foo.Context(…)` is exactly the right way.
Of course this won't work in multithreaded (or gevent/coroutine/etc.) code,
and it's inappropriate in various other cases, but if that's not an issue, in
some cases, this is fine.
Since you brought up multithreading in your comments: In the simple style of
multithreading where you have long-running jobs, the global style actually
works perfectly fine, with a trivial change—replace the global `Context` with
a global [`threading.local`](http://docs.python.org/library/threading.html)
instance that contains a `Context`. Even in the style where you have small
jobs handled by a thread pool, it's not much more complicated. You attach a
context to each job, and then when a worker pulls a job off the queue, it sets
the thread-local context to that job's context.
However, I'm not sure multithreading is going to be a good fit for your app
anyway. Multithreading is great in Python when your tasks occasionally have to
block for IO and you want to be able to do that without stopping other
tasks—but, thanks to the GIL, it's nearly useless for parallelizing CPU work,
and it sounds like that's what you're looking for. Multiprocessing (whether
via the `multiprocessing` module or otherwise) may be more of what you're
after. And with separate processes, keeping separate contexts is even simpler.
(Or, you can write thread-based code and switch it to multiprocessing, leaving
the `threading.local` variables as-is and only changing the way you spawn new
tasks, and everything still works just fine.)
It may make sense to provide a "context" in the context manager sense, as an
external version of the standard library's
[`decimal`](http://docs.python.org/library/decimal.html) module did, so
someone can write:
with foo.Context(…):
# do stuff under custom context
# back to default context
However, nobody could really think of a good use case for that (especially
since, at least in the naive implementation, it doesn't actually solve the
threading/etc. problem), so it wasn't added to the standard library, and you
may not need it either.
If you want to do this, it's pretty trivial. If you're using a private global,
just add this to your `Context` class:
def __enter__(self):
global _context
self._stashedcontext = _context
_context = self
def __exit__(self, *args):
global context
_context = self._stashedcontext
And it should be obvious how to adjust this to public, thread-local, etc.
alternatives.
Another alternative is to make everything a member of the `Context` object.
The top-level module functions then just delegate to the global context, which
has a reasonable default value. This is exactly how the standard library
[`random`](http://docs.python.org/library/random.html) module works—you can
create a `random.Random()` and call `randrange` on it, or you can just call
`random.randrange()`, which calls the same thing on a global default
`random.Random()` object.
If creating a `Context` is too heavy to do at import time, especially if it
might not get used (because nobody might ever call the global functions), you
can use the singleton pattern to create it on first access. But that's rarely
necessary. And when it's not, the code is trivial. For example, the
[source](http://hg.python.org/cpython/file/2.7/Lib/random.py) to `random`,
starting at line 881, does this:
_inst = Random()
seed = _inst.seed
random = _inst.random
uniform = _inst.uniform
…
And that's all there is to it.
And finally, as you suggested, you could make everything a member of a
different `Calculator` object which owns a `Context` object. This is the
traditional OOP solution; overusing it tends to make Python feel like Java,
but using it when it's appropriate is not a bad thing.
|
installing libjpeg for pil and Google app engine on mac Mountain Lion
Question: I'm sure there's a duplicate of this somewhere out there but I looked and am
about at the end of my rope. I'm trying get PIL working on my mac OS X 10.8 so
that I can use `dev_appserver.py` to test an imaging feature. First I had
trouble installing PIL until I got Homebrew and installed it using `brew
install pil`. I was under the opinion that brew installed all the necessary
dependencies but when I tried to resize a jpeg in my app, it says `IOError:
decoder jpeg is not available`. So I looked online and most places said I
needed to (1) uninstall PIL, (2) install libjpeg from source and (3) reinstall
PIL. So, I `brew uninstall PIL`, and then
curl -O www.ijg.org/files/jpegsrc.v7.tar.gz
tar zxvf jpegsrc.v7.tar.gz
cd jpeg-7d/
./configure
make
make install
and finally `brew install pil`. I restart dev_appserver.py and reload the page
on localhost, but same error. I tested pil out from the `python` command-line
with
>>> from PIL.Image import Image
>>> f = open("someimagefile", "rb")
>>> i = Image()
>>> i.fromstring(f.read(), decoder_name="jpeg")
Traceback blah blah blah
IOError: decoder jpeg not available
I don't have much experience installing utilities from command-line, so I
probably missed something obvious. Again, sorry if there are duplicates, but
like I said, I looked and couldn't find anything that seemed to work.
Answer: Finally got it working! Thanks to @zgoda and this
[link](https://sites.google.com/site/asidoothings/python-pil). Here are the
steps I ended up with for those of you who have the same problem:
First make sure PIL is not installed. Download libjpeg from
<http://www.ijg.org/files/jpegsrc.v8c.tar.gz>, unpacked it, `./configure`, and
`make`. When I tried to `make install` it couldn't find the directory to store
the man pages so installation failed. I looked at the information on the above
link and decided to
`cp -r ~/Downloads/jpeg-6d/ /usr/local/jpeg`
I suspect if the installation goes fine than that line isn't necessary.
Then edit the following line in PIL's setup.py:
JPEG_ROOT = None
to
JPEG_ROOT = "/usr/local/jpeg"
finally:
$ python setup.py build
$ python setup.py install
|
Issue with finding parent of a particular tag in html using python
Question: I am trying to fetch parent element of a particular tag using below mentioned
code:
# -*- coding: cp1252 -*-
import csv
import urllib2
import sys
import time
from bs4 import BeautifulSoup
from itertools import islice
page1= urllib2.urlopen('http://www.sfr.fr/mobile/telephones?vue=000029&tgp=toutes-les-offres&typesmartphone=se-android&typesmartphone=se-apple&typesmartphone=se-bada&typesmartphone=se-rim-blackberry&typesmartphone=se-windows&p=0').read()
soup1 = BeautifulSoup(page1)
price_parent = soup1.findParents('div')
print price_parent
**Problem:** Output which I am getting after running this code returns Null
array `[]`, if I use `findParent` instead of Parents then also it returns
`None` value.
My actual problem is similar to this [BeautifulSoup - findAll not within
certain tag](http://stackoverflow.com/questions/10777250/beautifulsoup-
findall-not-within-certain-tag)
To solve my actual problem I need to get parents of elements for which I am
getting `None` value as mentioned above.
Please help me in solving this issue and pardon my ignorance as I am new to
programming.
Answer: `.findParents()` does not do what you think it does. It finds the parents of
the _current element_ that match the search. You are trying to find the
parents of a page element, which is already the top-level element.
If you had a structure like this:
<html>
<body>
<div class="foo">
<span id="bar">Some text</span>
</div>
</body>
</html>
where `soup` is a BeautifulSoup variable for the whole structure, you can find
the `span` with:
spanelement = soup.find('span', id='bar')
and then calling `.findParent('div')` will return a result, namely the `<div
class="foo">` element.
So, calling `.findParents()` on a top-level element will _always_ return an
empty result, there _are no parents_. Call it on something that does have a
parent element instead.
|
How to store OAuth token for Github in a Python script?
Question: I am working on a Python script that access Github using basic authentication.
I want to use OAuth so that user doesn't have to enter credentials every time
he uses the script. Most importantly, user's password does not get saved in
the `.bash_history`.
This Github API has the code to get token using [Basic
authentication](http://developer.github.com/v3/oauth/#create-a-new-
authorization).
`curl -u $USER_NAME --silent https://api.github.com/authorizations`
User is asked to enter password and gets token in the response.
1. Now where do I save this token securely so that next time when the script is run user doesn't have to enter anything?
2. The aim is to avoid storing the password or asking the user to enter every time he uses the script. Is there some other way to achieve these?
Answer: You should probably save the token in a config file in the user's home
directory. Preferably, you can restrict permissions on the file to make sure
that only that user may access the config file.
|
Celery - Programmatically list workers
Question: How can I programmatically, using Python code, list current workers and their
corresponding `celery.worker.consumer.Consumer` instances?
Answer: You can use
[celery.control.inspect](http://docs.celeryproject.org/en/master/userguide/workers.html#inspecting-
workers) to inspect the running workers:
>>> import celery
>>> celery.current_app.control.inspect().ping()
{u'celery@host': {u'ok': u'pong'}}
|
Compare list of datetimes with datetime in Python
Question: I have a list of datetime objects and would like to find the ones which are
within a certain time frame:
import datetime
dates = [ datetime.datetime(2007, 1, 2, 0, 1),
datetime.datetime(2007, 1, 3, 0, 2),
datetime.datetime(2007, 1, 4, 0, 3),
datetime.datetime(2007, 1, 5, 0, 4),
datetime.datetime(2007, 1, 6, 0, 5),
datetime.datetime(2007, 1, 7, 0, 6) ]
#in reality this is a list of over 25000 dates
mask = (dates>datetime.datetime(2007,1,3)) & \
(dates<datetime.datetime(2007,1,6))
However, this results in the following error: "TypeError: can't compare
datetime.datetime to list"
How can I fix my code?
Answer: You can mask a
[`numpy.array`](http://docs.scipy.org/doc/numpy/reference/generated/numpy.array.html)
in the syntax you describe _(but not a list)_ :
import numpy as np
date1 = np.array(dates)
mask = (dates1 > datetime.datetime(2007,1,3)) & \
(dates1 < datetime.datetime(2007,1,6))
In [14]: mask
Out[14]: array([False, True, True, True, False, False], dtype=bool)
In [15]: dates1[mask]
Out[15]: array([2007-01-03 00:02:00, 2007-01-04 00:03:00, 2007-01-05 00:04:00], dtype=object)
_(since this question is tagged numpy, presumably this is what you were
intending.)_
|
Passing parameters to a webapp2.RequestHandler object in python
Question: Is there any way to pass parameters to a RequestHandler object when I create
my WSGIApplication instance?
I mean
app = webapp2.WSGIApplication([
('/', MainHandler),
('/route1', Handler1),
('/route2', Handler2)
], debug=True)
Is it possible to pass some arguments to `MainHandler`, `Handler1` or
`Handler2`?
Thanks in advance
Answer: You can also pass parameters through a configuration dictionary.
First you define a configuration:
import webapp2
config = {'foo': 'bar'}
app = webapp2.WSGIApplication(routes=[
(r'/', 'handlers.MyHandler'),
], config=config)
Then access it as you need. Inside a RequestHandler, for example:
import webapp2
class MyHandler(webapp2.RequestHandler):
def get(self):
foo = self.app.config.get('foo')
self.response.write('foo value is %s' % foo)
From here: [webapp2 v2.5.1 documentation](http://webapp-
improved.appspot.com/guide/app.html#guide-app-config)
|
Python - Convert negative decimals from string to float
Question: I need to read in a large number of .txt files, each of which contains a
decimal (some are positive, some are negative), and append these into 2 arrays
(genotypes and phenotypes). Subsequently, I wish to perform some mathematical
operations on these arrays in scipy, however the negative ('-') symbol is
causing problems. Specifically, I cannot convert the arrays to float, because
the '-' is being read as a string, causing the following error:
ValueError: could not convert string to float:
Here is my code as it's currently written:
import linecache
gene_array=[]
phen_array=[]
for i in genotype:
for j in phenotype:
genotype='/path/g.txt'
phenotype='/path/p.txt'
g=linecache.getline(genotype,1)
p=linecache.getline(phenotype,1)
p=p.strip()
g=g.strip()
gene_array.append(g)
phen_array.append(p)
gene_array=map(float,gene_array)
phen_array=map(float,phen_array)
I am fairly certain at this point that it is the negative sign that is causing
the problem, but it is not clear to me why. Is my use of Linecache the problem
here? Is there an alternative method that would be better?
The result of
print gene_array
is
['-0.0448022516321286', '-0.0236187263814157', '-0.150505384829925', '-0.00338459268479522', '0.0142429109897682', '0.0286253352284279', '-0.0462358095345649', '0.0286232317578776', '-0.00747425206137217', '0.0231790239373428', '-0.00266935581919541', '0.00825077426011094', '0.0272744527203547', '0.0394829854063242', '0.0233109171715023', '0.165841084392078', '0.00259693465334536', '-0.0342590874424289', '0.0124600520095644', '0.0713627590092807', '-0.0189374898081401', '-0.00112750710611284', '-0.0161387333242288', '0.0227226505624106', '0.0382173405035751', '0.0455518646388402', '-0.0453048799717046', '0.0168570746329513']
Answer: The issue seems to be with empty string or space as evident from your error
message
ValueError: could not convert string to float:
To make it work, convert the map to a list comprehension
gene_array=[float(e) for e in gene_array if e]
phen_array=[float(e) for e in phen_array if e]
By empty string means
`float(" ")` or `float("")` would give value errors, so if any of the items
within `gene_array` or `phen_array` has space, this will throw an error while
converting to float
There could be many reasons for empty string like
* empty or blank line
* blank line either at the beginning or end
|
why does python require __init__.py to treat directories as containing packages?
Question: While going through 6.4 Packages section of [python
manual](http://docs.python.org/2/tutorial/modules.html) I came across the
following line:
> The `__init__.py` files are required to make Python treat the directories as
> containing packages; this is done to prevent directories with a common name,
> such as string, from unintentionally hiding valid modules that occur later
> on the module search path.
I understand that `__init__.py` is required to mark directories as containing
packages, but I don't understand what it means by `prevent directories with a
common name...from unintentionally hiding valid modules...`.
Could someone explain why the `__init__.py` is required?
Answer: Lets say you had a project that contained a directory called `math` that
contained some numerical data. If no `__init__.py` were required, then when
you did `import math`, it would try to import that directory instead of the
real `math` module. But since your directory just contained data and not
actual Python code, the import would fail. Thus your `math` directory would
block you from importing the real `math` module from the standard library,
even though your `math` directory doesn't contain Python code at all.
The `__init__.py` is like a confirmation, the directory saying "Yes, I really
am a Python package, not just a directory full of files. It makes sense to
import me." Any directories that don't "announce" themselves in this way are
skipped over because Python knows they can't be imported. This is good,
because the Python standard library has modules with lots of common names (os,
math, time, symbol, resource, etc.). Without the `__init__.py` requirement,
you would never be able to use any of those names for _any_ directory on your
Python path -- not even to store data or files unrelated to Python.
`string` is actually not the best example in this case. There is a module
called `string` but it is not so useful these days because most of its
functions are available as methods on the `str` type. But, like I mentioned,
there are lots of other modules with common names.
|
IncompleteRead using httplib
Question: I have been having a persistent problem getting an rss feed from a particular
website. I wound up writing a rather ugly procedure to perform this function,
but I am curious why this happens and whether any higher level interfaces
handle this problem properly. This problem isn't really a show stopper, since
I don't need to retrieve the feed very often.
I have read a solution that traps the exception and returns the partial
content, yet since the incomplete reads differ in the amount of bytes that are
actually retrieved, I have no certainty that such solution will actually work.
#!/usr/bin/env python
import os
import sys
import feedparser
from mechanize import Browser
import requests
import urllib2
from httplib import IncompleteRead
url = 'http://hattiesburg.legistar.com/Feed.ashx?M=Calendar&ID=543375&GUID=83d4a09c-6b40-4300-a04b-f88884048d49&Mode=2013&Title=City+of+Hattiesburg%2c+MS+-+Calendar+(2013)'
content = feedparser.parse(url)
if 'bozo_exception' in content:
print content['bozo_exception']
else:
print "Success!!"
sys.exit(0)
print "If you see this, please tell me what happened."
# try using mechanize
b = Browser()
r = b.open(url)
try:
r.read()
except IncompleteRead, e:
print "IncompleteRead using mechanize", e
# try using urllib2
r = urllib2.urlopen(url)
try:
r.read()
except IncompleteRead, e:
print "IncompleteRead using urllib2", e
# try using requests
try:
r = requests.request('GET', url)
except IncompleteRead, e:
print "IncompleteRead using requests", e
# this function is old and I categorized it as ...
# "at least it works darnnit!", but I would really like to
# learn what's happening. Please help me put this function into
# eternal rest.
def get_rss_feed(url):
response = urllib2.urlopen(url)
read_it = True
content = ''
while read_it:
try:
content += response.read(1)
except IncompleteRead:
read_it = False
return content, response.info()
content, info = get_rss_feed(url)
feed = feedparser.parse(content)
As already stated, this isn't a mission critical problem, yet a curiosity, as
even though I can expect urllib2 to have this problem, I am surprised that
this error is encountered in mechanize and requests as well. The feedparser
module doesn't even throw an error, so checking for errors depends on the
presence of a 'bozo_exception' key.
Edit: I just wanted to mention that both wget and curl perform the function
flawlessly, retrieving the full payload correctly every time. I have yet to
find a pure python method to work, excepting my ugly hack, and I am very
curious to know what is happening on the backend of httplib. On a lark, I
decided to also try this with twill the other day and got the same httplib
error.
P.S. There is one thing that also strikes me as very odd. The IncompleteRead
happens consistently at one of two breakpoints in the payload. It seems that
feedparser and requests fail after reading 926 bytes, yet mechanize and
urllib2 fail after reading 1854 bytes. This behavior is consistend, and I am
left without explanation or understanding.
Answer: At the end of the day, all of the other modules (`feedparser`, `mechanize`,
and `urllib2`) call `httplib` which is where the exception is being thrown.
Now, first things first, I also downloaded this with wget and the resulting
file was 1854 bytes. Next, I tried with `urllib2`:
>>> import urllib2
>>> url = 'http://hattiesburg.legistar.com/Feed.ashx?M=Calendar&ID=543375&GUID=83d4a09c-6b40-4300-a04b-f88884048d49&Mode=2013&Title=City+of+Hattiesburg%2c+MS+-+Calendar+(2013)'
>>> f = urllib2.urlopen(url)
>>> f.headers.headers
['Cache-Control: private\r\n',
'Content-Type: text/xml; charset=utf-8\r\n',
'Server: Microsoft-IIS/7.5\r\n',
'X-AspNet-Version: 4.0.30319\r\n',
'X-Powered-By: ASP.NET\r\n',
'Date: Mon, 07 Jan 2013 23:21:51 GMT\r\n',
'Via: 1.1 BC1-ACLD\r\n',
'Transfer-Encoding: chunked\r\n',
'Connection: close\r\n']
>>> f.read()
< Full traceback cut >
IncompleteRead: IncompleteRead(1854 bytes read)
So it is reading all 1854 bytes but then thinks there is more to come. If we
explicitly tell it to read only 1854 bytes it works:
>>> f = urllib2.urlopen(url)
>>> f.read(1854)
'\xef\xbb\xbf<?xml version="1.0" encoding="utf-8"?><rss version="2.0" xmlns:atom="http://www.w3.org/2005/Atom">...snip...</rss>'
Obviously, this is only useful if we always know the exact length ahead of
time. We can use the fact the partial read is returned as an attribute on the
exception to capture the entire contents:
>>> try:
... contents = f.read()
... except httplib.IncompleteRead as e:
... contents = e.partial
...
>>> print contents
'\xef\xbb\xbf<?xml version="1.0" encoding="utf-8"?><rss version="2.0" xmlns:atom="http://www.w3.org/2005/Atom">...snip...</rss>'
[This blog post](http://bobrochel.blogspot.co.nz/2010/11/bad-servers-chunked-
encoding-and.html) suggests this is a fault of the server, and describes how
to monkey-patch the `httplib.HTTPResponse.read()` method with the
`try..except` block above to handle things behind the scenes:
import httplib
def patch_http_response_read(func):
def inner(*args):
try:
return func(*args)
except httplib.IncompleteRead, e:
return e.partial
return inner
httplib.HTTPResponse.read = patch_http_response_read(httplib.HTTPResponse.read)
I applied the patch and then `feedparser` worked:
>>> import feedparser
>>> url = 'http://hattiesburg.legistar.com/Feed.ashx?M=Calendar&ID=543375&GUID=83d4a09c-6b40-4300-a04b-f88884048d49&Mode=2013&Title=City+of+Hattiesburg%2c+MS+-+Calendar+(2013)'
>>> feedparser.parse(url)
{'bozo': 0,
'encoding': 'utf-8',
'entries': ...
'status': 200,
'version': 'rss20'}
This isn't the nicest way of doing things, but it seems to work. I'm not
expert enough in the HTTP protocols to say for sure whether the server is
doing things wrong, or whether `httplib` is mis-handling an edge case.
|
Twitter API Python Character Encoding
Question: I am experimenting with the Twitter API for Python and have run into a
character encoding/decoding issue; when I am collecting tweets for a user
(@BBCWorld in this instance), if there is _special_ punctuation I receive the
following error:
286952044814794753 : Traceback (most recent call last):
File "C:\Python27\lib\encodings\cp850.py", line 12, in encode
return codecs.charmap_encode(input,errors,encoding_map)
UnicodeEncodeError: 'charmap' codec can't encode character u'\u201c' in position 0: character maps to <undefined>
Note: The long number at the start is the ID of the tweet causing the error.
The specific character that is causing this problem is an angular (opening)
double quotation mark (like those used in MS-Word). Is there a way to display
such punctuation in a compatible form? Ideally I want to sanitise tweets to
overcome this kind of error by use of replacement, therefore maintaining
context, rather that omitting characters.
This is the core of the code:
tweets=api.GetUserTimeline('BBCWorld')
try:
for tweet in tweets:
print tweet.id, ": ", (tweet.text)
except UnicodeEncodeError as uee:
print uee
Thanks for any pointers,
Milutin
Answer: This problem does not seem to be an issue of python-twitter or python for that
matter - it's a problem with Windows cmd.
If you try this under a suitable Unix terminal, this is what you get:
>>> import twitter
>>> api = twitter.Api()
>>> print api.GetStatus('286952044814794753').text
“How do you change mindsets at a societal level, in a country of 1.2bn people?” - Viewpoints from India http://t.co/RiP4t71q #Delhigangrape
Take a look at this question for a discussion of how to deal with this under
Windows: [Unicode not printing correctly to cp850 (cp437), play card
suits](http://stackoverflow.com/questions/4233227/unicode-not-printing-
correctly-to-cp850-cp437-play-card-suits)
My best bet for you would be to change your console font and codepage to a
unicode compliant, as outlined here:
<http://stackoverflow.com/a/4234515/679897> or here:
<http://www.velocityreviews.com/forums/t717717-python-unicode-and-windows-cmd-
exe.html>
|
Importing Python Librarys over C#?
Question: So I'm new to Python and I work with IronPython in Visual Studio.
So in my C# Project I call the Python Script for executing some tasks. Now I
work in a bigger company and so a lot of File Paths etc. are different. And
I'm wondering if it's possible to pass the Python file a Path, and then import
the Modules (for example urlib) from this path.
So in C# with IronPython it's possible to execute a Python script with
var ipy = Python.CreateRuntime();
dynamic PYthon_Script = ipy.UseFile("test.py");
And in my Python SCript I got the following Code:
import sys
path = "C:\Program Files (x86)\IronPython 2.7\Lib"
sys.path.append(path)
import urllib
import httplib
...
So I was wondering if it's possible to pass a parameter for the variable path,
so sys.path.append(path) will change with the parameter given and the
libraries are imported correctly.
Answer: You just want to pass a parameter to the script? Sure, that's easy.
The main way to do that is by using `sys.argv`:
import sys
path = sys.argv[1]
sys.path.append(path)
import urllib
import httplib
Then instead of doing this:
py.exe myscript.py
You do this:
py.exe myscript.py "C:\Program Files (x86)\IronPython 2.7\Lib"
If you're running this directly from within a .NET launcher program, you can
also just insert the variable dynamically:
PYthon_Script.SetVariable("path", "C:\Program Files (x86)\IronPython 2.7\Lib")
Then, from within the script, you can use that variable.
Or you can even modify `sys.path` itself from the launcher. See the `Runtime`
docs for details.
If you want to add multiple paths, just change these two lines:
paths = sys.argv[1:]
sys.path.extend(paths)
If you want something that sticks around in your environment, so you don't
have to pass it every time, that's what environment variables are for.
There's actually a standard environment variable named `IRONPYTHONPATH` that
should work without you having to do anything. I've never used it myself, but
if it works, you don't need to do anything explicit in your code at all. Just
set it in your `cmd.exe` shell, in your Control Panel, in the C# program
you're launching `myscript.py` from, whatever's appropriate. [This
answer](http://stackoverflow.com/questions/3701646/how-to-add-to-the-
pythonpath-in-windows-7) has examples for the first two. (They're setting
`PYTHONPATH`, which affects CPython, instead of `IRONPYTHONPATH`, which
affects IronPython, but it should be obvious what to change.)
If that doesn't work, you can do the same thing manually:
import os
import sys
path = os.environ['MY_IRONPYTHON_EXTRA_PATH']
sys.path.append(path)
import urllib
import httplib
Now, you can set that `MY_IRONPYTHON_EXTRA_PATH` environment variable instead
of `IRONPYTHON_PATH`.
Here, because you just have a string instead of a list, if you want to specify
multiple paths, you need to add a separator. The standard path separator on
Windows is a semicolon. So:
paths = os.environ['MY_IRONPYTHON_EXTRA_PATH'].split(';')
sys.path.extend(paths)
|
When is __lldb_init_module called?
Question: I'm following WWDC session 412 - Debugging in Xcode. There is a demo there
about creating custom LLDB summaries for your own classes.
I simply can't get the summaries to show up.
By inserting print calls in the Python script I have been able to determine
that:
1. The script file is getting imported
2. __lldb_init_module is never called
Any idea about what could prevent __lldb_init_module from being called? Is
there a specific time when you need to import the script?
Answer: For me this worked by adding
command script import /path/to/CustomSummaries.py
to the `~/.lldbinit` file and restarting Xcode, or by setting a breakpoint in
"main" and executing the import command in the debugger console.
I tested it with a minimal custom description script:
import lldb
def myobject_summary(valueObject, dictionary):
return 'MyCustomDescription'
def __lldb_init_module(debugger, dict):
debugger.HandleCommand('type summary add MyObject -F CustomSummaries.myobject_summary')
and this is the view in the Xcode debugger window:
Note that you have to restart Xcode after changes to the script. It also seems
that the output of "print" statements in the init method is not shown if the
script is imported in the Xcode debugger console.
|
Python: compare list items to dictionary keys twice in one for loop?
Question: ## I'm stuck in a script I have to write and can't find a way out...
I have two files with partly overlapping information. Based on the information
in one file I have to extract info from the other and save it into multiple
new files. The first is simply a table with IDs and group information (which
is used for the splitting). The other contains the same IDs, but each twice
with slightly different information.
**What I'm doing:** I create a list of lists with ID and group informazion,
like this:
table = [[ID, group], [ID, group], [ID, group], ...]
Then, because the second file is huge and not sorted in the same way as the
first, I want to create a dictionary as index. In this index, I would like to
save the ID and where it can be found inside the file so I can quickly jump
there later. The problem there, of course, is that every ID appears twice. My
simple solution (but I'm in doubt about this) is adding an -a or -b to the ID:
index = {"ID-a": [FPos, length], "ID-b": [FPOS, length], "ID-a": [FPos, length], ...}
The code for this:
for line in file:
read = (line.split("\t"))[0]
if not (read+"-a") in indices:
index = read + "-a"
length = len(line)
indices[index] = [FPos, length]
else:
index = read + "-b"
length = len(line)
indices[index] = [FPos, length]
FPos += length
What I am wondering now is if the next step is actually valid (I don't get
errors, but I have some doubts about the output files).
for name in table:
head = name[0]
## first round
(FPos,length) = indices[head+"-a"]
file.seek(FPos)
line = file.read(length)
line = line.rstrip()
items = line.split("\t")
output = ["@" + head +" "+ "1:N:0:" +"\n"+ items[9] +"\n"+ "+" +"\n"+ items[10] +"\n"]
name.append(output)
##second round
(FPos,length) = indices[head+"-b"]
file.seek(FPos)
line = file.read(length)
line = line.rstrip()
items = line.split("\t")
output = ["@" + head +" "+ "2:N:0:" +"\n"+ items[9] +"\n"+ "+" +"\n"+ items[10] +"\n"]
name.append(output)
Is it ok to use a for loop like that?
Is there a better, cleaner way to do this?
Answer: Use a `defaultdict(list)` to save all your file offsets by ID:
from collections import defaultdict
index = defaultdict(list)
for line in file:
# ...code that loops through file finding ID lines...
index[id_value].append((fileposn,length))
The
[defaultdict](http://docs.python.org/2/library/collections.html#collections.defaultdict)
will take care of initializing to an empty list on the first occurrence of a
given id_value, and then the (fileposn,length) tuple will be appended to it.
This will accumulate all references to each id into the index, whether there
are 1, 2, or 20 references. Then you can just search through the given
fileposn's for the related data.
|
Converting nested JSON content dump to XLS
Question: I have a JSON dump from a content management site which follows the format:
[
{
id: "obj1",
children: [...]
},
{
id: "obj2",
children: [...]
}
]
There are 2-4 nesting levels.
What would be the best way to convert this to Microsoft Excel XLS so that
nested levels are handled somehow, for the Excel-able customer to play with
their data?
With this particular data, one way to do this would create a new sheet for
each top level folder (nesting level). All sheets would contain the same
column names picked from the JSON objects in that particular folder.
Are there any ready-made tools for importing JSON to Excel?
Preferably as a command-line tool and if scripting is required then in Python.
Answer: It depends on your data.
If the nesting happens without any kind of repetition then simplest option is
to replicate everything or leave blank spaces if your data is complete enough
to be able to assume a repetition where you find a blank.
This means the XLS as a CSV will look like this:
Element1 Element1.1 Element1.1.1 ...
Element1 Element1.1 Element1.1.2 ...
Element2 Element2.1 Element2.1.1 ...
Where each element is a child of the one at its left. You can see a parent
repeats as many times as children it has multiplied by how many times does
each of the children appear.
You can also do a very simple table with two columns:
**Parent** **Child**
Element1 Element1.1
Element1.1 Element1.1.1
Element1.1 Element1.1.2
Element2 Element2.1
Element2.1 Element2.1.1
...
What an element is depends on your granularity. You can group pairs of
key=values as a string, you can group several fields into one and parse it
back with regular expressions, or you can separate everything and consider the
key as an element and the value as another one.
Finally, if there is some regularity then you can take a more interesting
approach, assume you have some repeating fieldnames, in that case you can take
any of the previous approaches but using the fieldnames to generate a matrix
instead of a list. The first example is trivial since it is obviously a tuple
list that does already have an implicit ordinal header, the second one is a
table and may look like a matrix already, but you can do this.
**Parent** **Child (default)** **Repeating key1** **Repeating key2**
e1 e1.1
e1.1 e1.1.1
e.1.1.1 something
e.1.1 e.1.1.2
e.1.1.2 somethingelse
So basically in the end you have a sparse matrix.
There are very interesting ways to store matrixes with three dimensions using
several sheets on an XLS, but human-readability may drop with it. It boils
down to the data you are using, **there is no general solution**.
|
Memory leak in tornado generator engine with try/finally block when connections are closed
Question: This awesome code, shows memory leak in tornado's `gen` module, when
connections are closed without reading the response:
import gc
from tornado import web, ioloop, gen
class MainHandler(web.RequestHandler):
@web.asynchronous
@gen.engine
def get(self):
gc.collect()
print len(gc.garbage) # print zombie objects count
self.a = '*' * 500000000 # ~500MB data
CHUNK_COUNT = 100
try:
for i in xrange(CHUNK_COUNT):
self.write('*' * 10000) # write ~10KB of data
yield gen.Task(self.flush) # wait for reciever to recieve
print 'finished'
finally:
print 'finally'
application = web.Application([
(r"/", MainHandler),
])
application.listen(8888)
ioloop.IOLoop.instance().start()
and now, run a simple test client, multiple times
#!/usr/bin/python
import urllib
urlopen('http://127.0.0.1:8888/') # exit without reading response
Now, server output shows, incremental memory usage:
0
WARNING:root:Write error on 8: [Errno 104] Connection reset by peer
1
WARNING:root:Read error on 8: [Errno 104] Connection reset by peer
WARNING:root:error on read
Traceback (most recent call last):
File "/usr/local/lib/python2.7/dist-packages/tornado-2.4.1-py2.7.egg/tornado/iostream.py", line 361, in _handle_read
if self._read_to_buffer() == 0:
File "/usr/local/lib/python2.7/dist-packages/tornado-2.4.1-py2.7.egg/tornado/iostream.py", line 428, in _read_to_buffer
chunk = self._read_from_socket()
File "/usr/local/lib/python2.7/dist-packages/tornado-2.4.1-py2.7.egg/tornado/iostream.py", line 409, in _read_from_socket
chunk = self.socket.recv(self.read_chunk_size)
error: [Errno 104] Connection reset by peer
2
ERROR:root:Uncaught exception GET / (127.0.0.1)
HTTPRequest(protocol='http', host='127.0.0.1:8888', method='GET', uri='/', version='HTTP/1.0', remote_ip='127.0.0.1', body='', headers={'Host': '127.0.0.1:8888', 'User-Agent': 'Python-urllib/1.17'})
Traceback (most recent call last):
File "/usr/local/lib/python2.7/dist-packages/tornado-2.4.1-py2.7.egg/tornado/web.py", line 1021, in _stack_context_handle_exception
raise_exc_info((type, value, traceback))
File "/usr/local/lib/python2.7/dist-packages/tornado-2.4.1-py2.7.egg/tornado/web.py", line 1139, in wrapper
return method(self, *args, **kwargs)
File "/usr/local/lib/python2.7/dist-packages/tornado-2.4.1-py2.7.egg/tornado/gen.py", line 120, in wrapper
runner.run()
File "/usr/local/lib/python2.7/dist-packages/tornado-2.4.1-py2.7.egg/tornado/gen.py", line 345, in run
yielded = self.gen.send(next)
File "test.py", line 10, in get
self.a = '*' * 500000000
MemoryError
ERROR:root:500 GET / (127.0.0.1) 3.91ms
If you set `CHUNK_COUNT` to 1, the 10KB of data can be written to OS
connection buffer, and 'finished' and 'finally' texts will be printed to
console, and because generator is completed, no memory leak occurs.
**But the strange part** is that if your remove the try/finally block, the
problem disappears!! (even with `CHUNK_COUNT` set to 100)
Is this a bug on CPython or tornado or ...?!
Answer: This bug tested with Tornado 2.4.1 (the latest version when this question
asked), and reported on <https://github.com/facebook/tornado/issues/660> .
The problem fixed in commit
<https://github.com/facebook/tornado/commit/769bc52e11656788782a6e7a922ef646503f9ab0>
and included in Tornado 3.0.
|
socket programming in python doubts
Question: i am having trouble and a lot of questions about socket programming attached
code below ( all parts have been taken from the and written together) i am
trying to send mouse data to the client ,howver getting the error:
Traceback (most recent call last):
File "srvr.py", line 29, in <module>
serv.sendall(status)
File "/usr/lib/python2.7/socket.py", line 224, in meth
return getattr(self._sock,name)(*args)
TypeError: must be string or buffer, not int
Questions: 1.how do we send data over sockets other then strings or
specifically without the .send("...") statement .continously changing data??
2.what things should be kept in mind when sending stream of data?? 3.code
written here is a mess, would gladly appreciate help to teach some code sense
into me
Thank YOu
Code: server side:
from socket import * #import the socket library
##let's set up some constants
HOST = '' #we are the host
PORT = 29876 #arbitrary port not currently in use
ADDR = (HOST,PORT) #we need a tuple for the address
BUFSIZE = 4096 #reasonably sized buffer for data
## now we create a new socket object (serv)
## see the python docs for more information on the socket types/flags
serv = socket( AF_INET,SOCK_STREAM)
##bind our socket to the address
serv.bind((ADDR)) #the double parens are to create a tuple with one element
serv.listen(5)
print 'listening...'
conn,addr = serv.accept() #accept the connection
print '...connected!'
mouse = file('/dev/input/mouse0')
while True:
status, dx, dy = tuple(ord(c) for c in mouse.read(3))
def to_signed(n):
return n - ((0x80 & n) << 1)
dx = to_signed(dx)
dy = to_signed(dy)
conn.send(status)
conn.close()
client:
##client.py
from socket import *
HOST = 'localhost'
PORT = 29876 #our port from before
ADDR = (HOST,PORT)
BUFSIZE = 4096
cli = socket( AF_INET,SOCK_STREAM)
cli.connect((ADDR))
data = cli.recv(BUFSIZE)
while data != '':
print data
cli.close()
Answer: While transferring data over network, it is very usual to pack it according to
the big-endian byte order. Even though you have only three separates bytes at
a time, and thus byte ordering doesn't matter, I still prefer to pack and
unpack simply because it is a common way to communicate. Also, a common thing
to do, when receiving network data, is to check whether you actually received
the amount you were expecting, otherwise you have to request for more data.
For simplicity, consider the following function for that:
def recv(sock, size):
data = ''
to_receive = size
while to_receive > 0:
data += sock.recv(to_receive)
to_receive = size - len(data)
return data
Now, what is lacking in your code is a common protocol. The client is acting
as a receiver of raw meaningless data. Instead, it should be acting as a
receiver of triplets. Besides that, I suggest to let the client request how
many triplets he wants. Taking this into consideration, that is how I would
change your client code to:
import sys
import socket
import struct
serv_host = ''
serv_port = 29876
s = socket.socket(socket.AF_INET, socket.SOCK_STREAM)
s.connect((serv_host, serv_port))
# Tell the server how many triplets I want.
amount = int(sys.argv[1])
s.sendall(struct.pack('!i', amount))
pack_size = struct.calcsize('!bbb')
while amount:
status, dx, dy = struct.unpack('!bbb', recv(s, pack_size))
print status, dx, dy
amount -= 1
s.close()
Now the server also needs to respect this newly imposed protocol. Note that a
negative value effectively makes the client receive infinite triplets, that is
intentional. Here is the modified server:
import socket
import struct
def to_signed(n):
return n - ((0x80 & n) << 1)
mouse = open('/dev/input/mouse0')
host = ''
port = 29876
backlog = 5
s = socket.socket(socket.AF_INET, socket.SOCK_STREAM)
s.setsockopt(socket.SOL_SOCKET, socket.SO_REUSEADDR, 1)
s.bind((host, port))
s.listen(backlog)
print 'Listening'
while True:
client, address = s.accept()
# Obtain the number of triplets the client wants.
amount = struct.unpack('!i', recv(client, 4))[0]
while amount: # Send the triplets as they become available.
status, dx, dy = map(ord, mouse.read(3))
dx, dy = to_signed(dx), to_signed(dy)
print status, dx, dy
client.sendall(struct.pack('!bbb', status, dx, dy))
amount -= 1
client.close()
|
How to use multiprocessing with class instances in Python?
Question: I am trying to create a class than can run a separate process to go do some
work that takes a long time, launch a bunch of these from a main module and
then wait for them all to finish. I want to launch the processes once and then
keep feeding them things to do rather than creating and destroying processes.
For example, maybe I have 10 servers running the dd command, then I want them
all to scp a file, etc.
My ultimate goal is to create a class for each system that keeps track of the
information for the system in which it is tied to like IP address, logs,
runtime, etc. But that class must be able to launch a system command and then
return execution back to the caller while that system command runs, to
followup with the result of the system command later.
My attempt is failing because I cannot send an instance method of a class over
the pipe to the subprocess via pickle. Those are not pickleable. I therefore
tried to fix it various ways but I can't figure it out. How can my code be
patched to do this? What good is multiprocessing if you can't send over
anything useful?
Is there any good documentation of multiprocessing being used with class
instances? The only way I can get the multiprocessing module to work is on
simple functions. Every attempt to use it within a class instance has failed.
Maybe I should pass events instead? I don't understand how to do that yet.
import multiprocessing
import sys
import re
class ProcessWorker(multiprocessing.Process):
"""
This class runs as a separate process to execute worker's commands in parallel
Once launched, it remains running, monitoring the task queue, until "None" is sent
"""
def __init__(self, task_q, result_q):
multiprocessing.Process.__init__(self)
self.task_q = task_q
self.result_q = result_q
return
def run(self):
"""
Overloaded function provided by multiprocessing.Process. Called upon start() signal
"""
proc_name = self.name
print '%s: Launched' % (proc_name)
while True:
next_task_list = self.task_q.get()
if next_task is None:
# Poison pill means shutdown
print '%s: Exiting' % (proc_name)
self.task_q.task_done()
break
next_task = next_task_list[0]
print '%s: %s' % (proc_name, next_task)
args = next_task_list[1]
kwargs = next_task_list[2]
answer = next_task(*args, **kwargs)
self.task_q.task_done()
self.result_q.put(answer)
return
# End of ProcessWorker class
class Worker(object):
"""
Launches a child process to run commands from derived classes in separate processes,
which sit and listen for something to do
This base class is called by each derived worker
"""
def __init__(self, config, index=None):
self.config = config
self.index = index
# Launce the ProcessWorker for anything that has an index value
if self.index is not None:
self.task_q = multiprocessing.JoinableQueue()
self.result_q = multiprocessing.Queue()
self.process_worker = ProcessWorker(self.task_q, self.result_q)
self.process_worker.start()
print "Got here"
# Process should be running and listening for functions to execute
return
def enqueue_process(target): # No self, since it is a decorator
"""
Used to place an command target from this class object into the task_q
NOTE: Any function decorated with this must use fetch_results() to get the
target task's result value
"""
def wrapper(self, *args, **kwargs):
self.task_q.put([target, args, kwargs]) # FAIL: target is a class instance method and can't be pickled!
return wrapper
def fetch_results(self):
"""
After all processes have been spawned by multiple modules, this command
is called on each one to retreive the results of the call.
This blocks until the execution of the item in the queue is complete
"""
self.task_q.join() # Wait for it to to finish
return self.result_q.get() # Return the result
@enqueue_process
def run_long_command(self, command):
print "I am running number % as process "%number, self.name
# In here, I will launch a subprocess to run a long-running system command
# p = Popen(command), etc
# p.wait(), etc
return
def close(self):
self.task_q.put(None)
self.task_q.join()
if __name__ == '__main__':
config = ["some value", "something else"]
index = 7
workers = []
for i in range(5):
worker = Worker(config, index)
worker.run_long_command("ls /")
workers.append(worker)
for worker in workers:
worker.fetch_results()
# Do more work... (this would actually be done in a distributor in another class)
for worker in workers:
worker.close()
Edit: I tried to move the `ProcessWorker` class and the creation of the
multiprocessing queues outside of the `Worker` class and then tried to
manually pickle the worker instance. Even that doesn't work and I get an error
> RuntimeError: Queue objects should only be shared between processes through
> inheritance
. But I am only passing references of those queues into the worker instance??
I am missing something fundamental. Here is the modified code from the main
section:
if __name__ == '__main__':
config = ["some value", "something else"]
index = 7
workers = []
for i in range(1):
task_q = multiprocessing.JoinableQueue()
result_q = multiprocessing.Queue()
process_worker = ProcessWorker(task_q, result_q)
worker = Worker(config, index, process_worker, task_q, result_q)
something_to_look_at = pickle.dumps(worker) # FAIL: Doesn't like queues??
process_worker.start()
worker.run_long_command("ls /")
Answer: So, the problem was that I was assuming that Python was doing some sort of
magic that is somehow different from the way that C++/fork() works. I somehow
thought that Python only copied the class, not the whole program into a
separate process. I seriously wasted days trying to get this to work because
all of the talk about pickle serialization made me think that it actually sent
everything over the pipe. I knew that certain things could not be sent over
the pipe, but I thought my problem was that I was not packaging things up
properly.
This all could have been avoided if the Python docs gave me a 10,000 ft view
of what happens when this module is used. Sure, it tells me what the methods
of multiprocess module does and gives me some basic examples, but what I want
to know is what is the "Theory of Operation" behind the scenes! Here is the
kind of information I could have used. Please chime in if my answer is off. It
will help me learn.
When you run start a process using this module, the whole program is copied
into another process. But since it is not the "`__main__`" process and my code
was checking for that, it doesn't fire off yet another process infinitely. It
just stops and sits out there waiting for something to do, like a zombie.
Everything that was initialized in the parent at the time of calling
multiprocess.Process() is all set up and ready to go. Once you put something
in the multiprocess.Queue or shared memory, or pipe, etc. (however you are
communicating), then the separate process receives it and gets to work. It can
draw upon all imported modules and setup just as if it was the parent.
However, once some internal state variables change in the parent or separate
process, those changes are isolated. Once the process is spawned, it now
becomes your job to keep them in sync if necessary, either through a queue,
pipe, shared memory, etc.
I threw out the code and started over, but now I am only putting one extra
function out in the `ProcessWorker`, an "execute" method that runs a command
line. Pretty simple. I don't have to worry about launching and then closing a
bunch of processes this way, which has caused me all kinds of instability and
performance issues in the past in C++. When I switched to launching processes
at the beginning and then passing messages to those waiting processes, my
performance improved and it was very stable.
BTW, I looked at this link to get help, which threw me off because the example
made me think that methods were being transported across the queues:
<http://www.doughellmann.com/PyMOTW/multiprocessing/communication.html> The
second example of the first section used "next_task()" that appeared (to me)
to be executing a task received via the queue.
|
convert date to number python
Question: > **Possible Duplicate:**
> [Fetching datetime from float and vice versa in
> python](http://stackoverflow.com/questions/6706231/fetching-datetime-from-
> float-and-vice-versa-in-python)
Like many people I switched from `Matlab` to `Python`. `Matlab` represents
each date as a number. (`Integers` being days since `00-00-0000`, and
fractions being time in the day). I believe that `python` does the same except
off a different start date `0-0-0001`
I have been playing around with `datetime`, but cant seem to get away from
`datetime` objects and `timedeltas`. I am sure this is dead simple, but how do
I work with plain old numbers (floats)?
perhaps as a bit of context:
i bring in a date and time stamp and concatenate them to make one time value:
from datetime import datetime
date_object1 = datetime.strptime(date[1][0] + ' ' + date[1][1], '%Y-%m-%d %H:%M:%S')
date_object2 = datetime.strptime(date[2][0] + ' ' + date[2][1], '%Y-%m-%d %H:%M:%S')
Answer: Try this out:
import time
from datetime import datetime
t = datetime.now()
t1 = t.timetuple()
print time.mktime(t1)
It prints out a decimal representation of your date.
|
How do I check gnome-shell notifications with Python?
Question: I'm having quite some trouble doing that :
I'm using Conky on my Archlinux distro and coded a quick script in python to
check if I have a new mail in my gmail. In my conkyrc this script executes
every 5 minutes and returns a number of mails (0 if I don't have any). Works
fine.
What I wanted to do is :
If the number of mail is > 0 then display a notification (a gnome-shell
notification). The only problem I have now is that if I have unread mails (for
example 4 mails unread), each 5 minutes, there will be a NEW notification
saying that I have 4 mails unread. What I would like to do is checking if
there is already a notification so that I don't have to display it again...
Does anyone know how to solve that kind of problem ?
Here is my code :
#!/usr/bin/python
from gi.repository import Notify
from urllib.request import FancyURLopener
url = 'https://%s:%[email protected]/mail/feed/atom' % ("username", "password")
opener = FancyURLopener()
page = opener.open(url)
contents = page.read().decode('utf-8')
ifrom = contents.index('<fullcount>') + 11
ito = contents.index('</fullcount>')
unread = contents[ifrom:ito]
print(unread)
if unread != "0" :
Notify.init ("New Mail")
Hello=Notify.Notification.new ("New mail","You have "+unread+" new mail(s)","/usr/share/icons/Faenza/actions/96/mail-forward.png")
Hello.show ()
I must precise that I'm quite new to python. Thanks in advance if anyone got a
solution :)
Answer: One possible solution is serialise the value of unread into a file.
Then change your check from if the number of mails is greater than 0, to if
the number of mails is greater than zero or different from the last serialised
count from file.
An extension of this is to also serialise the time when a notification is run
along with the mail count, this way you extend the check to show the repeat
notification (showing 4 emails twice, not every 5 minutes say, but every 3
hours).
So your original check was `if unread != "0" :` it would become something like
`if unread != "0" && unread != serialisedvalue:` . In the show repeat
notification time threshold case it becomes
if unread != "0":
if ((datetime.now() - serialiseddate) < threshold) :
if unread != serialisedvalue:
Where `threshold = 3600*3` is for 3 hours.
Sample code for serialising and deserialising is below
#Serialising
try:
# This will create a new file or **overwrite an existing file**.
f = open("mailcount.txt", "w")
try:
f.write(unread + "\n") # Write a string to a file
f.write(datetime.now().strftime('%b %d %Y %I:%M%p'))
finally:
f.close()
except IOError:
pass
#Deserialising
try:
f = open("mailcount.txt", "r")
try:
# Read the entire contents of a file at once.
serialisedvalue = f.readline()
serialseddate = datetime.strptime(f.readline(), '%b %d %Y %I:%M%p')
finally:
f.close()
except IOError:
pass
Another possible solution would be to get the current active notification
count somehow and add that to your condition, though I couldn't find a method
for doing that using the [API that Notify
uses](http://developer.gnome.org/libnotify/0.7/).
|
Reading Chinese characters in a file and sending them to a browser
Question: I'm trying to make a program that:
* reads a list of Chinese characters from a file, makes a dictionary from them (associating a sign with its meaning).
* picks a random character and sends it to the browser using the `BaseHTTPServer` module when it gets a GET request.
Once I managed to read and store the signs properly (I tried writing them into
another file to check that I got them right and it worked) I couldn't figure
out how to send them to my browser.
I connect to 127.0.0.1:4321 and the best I've managed is to get a (supposedly)
url-encoded Chinese character, with its translation.
Code:
# -*- coding: utf-8 -*-
import codecs
from BaseHTTPServer import HTTPServer, BaseHTTPRequestHandler
from SocketServer import ThreadingMixIn
import threading
import random
import urllib
source = codecs.open('./signs_db.txt', 'rb', encoding='utf-16')
# Checking utf-16 works fine with chinese characters and stuff :
#out = codecs.open('./test.txt', 'wb', encoding='utf-16')
#for line in source:
# out.write(line)
db = {}
next(source)
for line in source:
if not line.isspace():
tmp = line.split('\t')
db[tmp[0]] = tmp[1].strip()
class Handler(BaseHTTPRequestHandler):
def do_GET(self):
self.send_response(200)
self.end_headers()
message = threading.currentThread().getName()
rKey = random.choice(db.keys())
self.wfile.write(urllib.quote(rKey.encode("utf-8")) + ' : ' + db[rKey])
self.wfile.write('\n')
return
class ThreadedHTTPServer(ThreadingMixIn, HTTPServer):
"""Handle requests in a separate thread."""
if __name__ == '__main__':
server = ThreadedHTTPServer(('localhost', 4321), Handler)
print 'Starting server, use <Ctrl-C> to stop'
server.serve_forever()
If I don't urlencode the chinese character, I get an error from python :
self.wfile.write(rKey + ' : ' + db[rKey])
Which gives me this:
> UnicodeEncodeError : 'ascii' codec can't encode character u'\u4e09' in
> position 0 : ordinal not in range(128)
I've also tried encoding/decoding with 'utf-16', and I still get that kind of
error messages.
Here is my test file:
Sign Translation
一 One
二 Two
三 Three
四 Four
五 Five
六 Six
七 Seven
八 Eight
九 Nine
十 Ten
So, my question is: "How can I get the Chinese characters coming from my
script to display properly in my browser"?
Answer: Declare the encoding of your page by writing a meta tag and make sure to
encode the entire Unicode string in UTF-8:
self.wfile.write(u'''\
<html>
<headers>
<meta http-equiv="content-type" content="text/html;charset=UTF-8">
</headers>
<body>
{} : {}
</body>
</html>'''.format(rKey,db[rKey]).encode('utf8'))
And/or declare the HTTP content type:
self.send_response(200)
self.send_header('Content-Type','text/html; charset=utf-8')
self.end_headers()
|
Is it possible to push data from Excel sheet using Python into a database?
Question: I have a requirement where using Python I need to write into excel cell , the
data which i will be collecting from web page.
But not getting an option how to do that.
any idea from you people?
_**As per @Marcin comments here is the more clear requirement I am looking
for_**
**Why is python a requirement?** -> _Yes I am using Python with Beautiful Soup
module to fetch data from web page._
**Where is excel running, or is it running at all?** -> _Excel is needed when
a script would complete its data collection from the web page,and will take an
attempt to the next page to do the same tasks,I want the current data to be
saved into an excel format._
**How is this related to the web? What exactly are you trying to achieve?**
_Hope this answer is given to the above question of your._
**Could you just work with a CSV file?** _Yes,I can work with it,but my final
goal is to push the data back to an database,which could be an Oracle or
Access database._
**_Architecture_**
------------------
| web |
| page |
------------------
|
|
|
Python and BS4(Data Extraction)
|
|
|
------------------
| Excel |
| data |
------------------
|
|
|
Python to Push Data(Oracle/Access)
|
|
|
------------------
| Any |
| DB |
------------------
**EDIT**
**As per @Thang**
I have tried but getting the error:
Microsoft Windows [Version 6.1.7600]
Copyright (c) 2009 Microsoft Corporation. All rights reserved.
C:\Users\Happy>python
Python 2.7.3 (default, Apr 10 2012, 23:31:26) [MSC v.1500 32 bit (Intel)] on win
32
Type "help", "copyright", "credits" or "license" for more information.
>>> import win32com.client
Traceback (most recent call last):
File "<stdin>", line 1, in <module>
ImportError: No module named win32com.client
>>>
Answer: You have a few options, actually, depending on what exactly you're trying to
do.
[`xlwt`](https://secure.simplistix.co.uk/svn/xlwt/trunk/xlwt/doc/xlwt.html) \-
I think this is great for manipulating Excel files from Python. I've linked
you to the documentation. [DataNitro](https://datanitro.com/) \- for Python
scripting from within Excel. It's a little slow, but I've used it plenty. You
are able to (with VBA in general) have Excel make a web request and pull in a
table. Before I knew how to program, that was how I did all of my web
scraping.
|
Importing class from another file in python - I know the fix, but why doesn't the original work?
Question: I can make this code work, but I am still confused why it won't work the first
way I tried.
I am practicing python because my thesis is going to be coded in it (doing
some cool things with Arduino and PC interfaces). I'm trying to import a class
from another file into my main program so that I can create objects. Both
files are in the same directory. It's probably easier if you have a look at
the code at this point.
#from ArduinoBot import *
#from ArduinoBot import ArduinoBot
import ArduinoBot
# Create ArduinoBot object
bot1 = ArduinoBot()
# Call toString inside bot1 object
bot1.toString()
input("Press enter to end.")
Here is the very basic ArduinoBot class
class ArduinoBot:
def toString(self):
print ("ArduinoBot toString")
Either of the first two commented out import statements will make this work,
but not the last one, which to me seems the most intuitive and general.
There's not a lot of code for stuff to go wrong here, it's a bit frustrating
to be hitting these kind of finicky language specific quirks when I had heard
some many good things about Python. Anyway I must be doing something wrong,
but why doesn't the simple 'import ClassName' or 'import FileName' work?
Thank you for your help.
Answer: consider a file (`example.py`):
class foo(object):
pass
class bar(object):
pass
class example(object):
pass
Now in your main program, if you do:
import example
what should be imported from the file `example.py`? Just the class `example`?
should the class `foo` come along too? The meaning would be too ambiguous if
`import module` pulled the whole module's namespace directly into your current
namespace.
The idea is that namespaces are wonderful. They let you know where the
class/function/data came from. They also let you group related things together
(or equivalently, they help you keep unrelated things separate!). A module
sets up a namespace and you tell python exactly how you want to bring that
namespace into the current context (namespace) by the way you use `import`.
`from ... import *` says -- bring everything in that module directly into my
namespace.
`from ... import ... as ...` says, bring only the thing that I specify
directly into my namespace, but give it a new name here.
Finally, `import ...` simply says bring that module into the current
namespace, but keep it separate. This is the most common form in production
code because of (at least) 2 reasons.
* It prevents name clashes. You can have a local class named `foo` which won't conflict with the `foo` in `example.py` \-- You get access to that via `example.foo`
* It makes it easy to trace down which module a class came from for debugging.
consider:
from foo import *
from bar import *
a = AClass() #did this come from foo? bar? ... Hmmm...
* * *
In this case, to get access to the class `example` from `example.py`, you
could also do:
import example
example_instance = example.example()
but you can also get `foo`:
foo_instance = example.foo()
|
Python regex: Multiple matches in one line (using findall())
Question: I'm looking for these "tags" inside text: `{t d="var1"}var2{/t}` or `{t
d="varA"}varB{/t}` There can be more attributes, only "d" is mandatory: `{t
d="var1" foo="bar"}var2{/t}`
My problem is - if there are more tags on one line, just one result is
returned, not all of them. What is returned (from test string below):
`(u'single1', u'Required item3')`
What I expect to be returned: `(u'single1', u'required1') (u'single2',
u'Required item2') (u'single3', u'Required item3') ` I got stuck with this. It
works with one tag per line but doesn't with more tags per one line.
# -*- coding: UTF-8 -*-
import re
test_string = u'''
<span><img src="img/ico/required.png" class="icon" alt="{t d="single1"}required1{/t}" title="{t d="single2"}Required item2{/t}" /> {t d="single3"}Required item3{/t}</span>
'''
re_pattern = '''
\{t[ ]{1} # start tag name
d=" # "d" attribute
([a-zA-Z0-9]*) # "d" attribute content
".*\} # end of "d" attribute
(.+) # tag content
\{/t\} # end tag
'''
rec_pattern = re.compile(re_pattern, re.VERBOSE)
res = rec_pattern.findall(test_string)
if res is not None:
for item in res:
print item
Answer: Your wildcards are greedy. Change them from `.*` to `.*?` so they'll be non-
greedy:
re_pattern = '''
\{t[ ]{1} # start tag name
d=" # "d" attribute
([a-zA-Z0-9]*) # "d" attribute content
".*?\} # end of "d" attribute
(.+?) # tag content
\{/t\} # end tag
'''
|
python can not find attribute Thread
Question: my python code like this:
#!/usr/bin/env python
import threading
from time import sleep,ctime
loops=[4,2]
def loop(nloop,nsec):
print 'start loop',nloop,'at:',ctime()
sleep(nsec)
print 'loop',nloop,'done at:',ctime()
def main():
print 'starting at:',ctime()
threads=[]
nloops = range(len(loops))
for i in nloops:
t = threading.Thread(target = loop, args = (i,loops[i]))
threads.append(t)
for i in nloops:
threads[i].start()
for i in nloops:
threads[i].join()
print 'all Done at:',ctime()
if __name__ == '__main__':
main()
but python output is:
t = threading.Thread(target = loop, args = (i,loops[i]))
AttributeError: 'module' object has no attribute 'Thread'
Exception AttributeError: '_shutdown' in <module 'threading'
i reinstall python ,but this issue still have ,how to fix it?
Answer: I bet you have a local file named `threading.py`, and it's masking the system
`threading` module.
You can verify this by printing `threading.__file__`:
import threading
print threading.__file__
to get the file path of the module that is being imported.
Rename it, or delete it, to fix this.
|
Install TortoiseHg for mac : No module named mercurial
Question: I'm trying to install TortoiseHg for Mac following these instructions :
<https://bitbucket.org/tortoisehg/thg/wiki/developers/MacOSX#!alternative-
install-via-macports>
I'm trying to follow the instructions about the "Alternative: Install via
Homebrew" and I have an issue.
When I execute `./thg log` as in the instructions it works, TortoiseHg is
launching. However when I try to create an App from the python script, the App
is created but when I launch it it crashes.
Here is the output :
Traceback (most recent call last):
File "/Users/fabienhenon/Documents/thg-mac-app/dist/TortoiseHg.app/Contents/Resources/__boot__.py", line 316, in <module>
_run()
File "/Users/fabienhenon/Documents/thg-mac-app/dist/TortoiseHg.app/Contents/Resources/__boot__.py", line 311, in _run
exec(compile(source, path, 'exec'), globals(), globals())
File "/Users/fabienhenon/Documents/thg-mac-app/dist/TortoiseHg.app/Contents/Resources/main.py", line 28, in <module>
imp.load_source("thg", SCRIPT_DIR + "/bin/thg")
File "/Users/fabienhenon/Documents/thg-mac-app/dist/TortoiseHg.app/Contents/Resources/bin/thg", line 56, in <module>
from mercurial import demandimport
ImportError: No module named mercurial
2013-01-06 12:25:17.436 TortoiseHg[406:707] TortoiseHg Error
logout
[Opération terminée]
When I type : `hg --version` I have the following output :
Mercurial Distributed SCM (version 2.4.2+20130102)
(see http://mercurial.selenic.com for more information)
Copyright (C) 2005-2012 Matt Mackall and others
This is free software; see the source for copying conditions. There is NO
warranty; not even for MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.
Can somebody help me with this issue ?
Thank you for your answers
Answer: I've found a solution to solve this issue.
From the error message I had, the script could not find the module named
mercurial. I'm new with Python so I had to make some researches to know how
module importation works and I found something about dynamically importing a
module using the `'sys'` module.
My solution was to edit the tortoisehg source code (the file where the error
came from) to dynamically add the path to my mercurial module to the
`'sys.path'` so that the program knows where to find the mercurial module.
Here is the code (in the 'thg' python file, line 56 (as mentioned by the
error)) :
import sys
sys.path.append("/Library/Python/2.7/site-packages")
You have to add this code just before this line :
from mercurial import demandimport
And the path must correspond to the location of your mercurial folder.
|
Python how do I overlay random images over images being generated to end up with 2 images with text
Question: Here is my code that I have so far. What it does is grabs a random text line
from the text file an generates a random color then creates the JPG image with
the text on top. What I want to do is take a random picture and overlay it on
top of the solid color at opacity of maybe 0.2 or something then put the text
on top of that so I end up with > solid color > picture overlayed > text on
top. This code generates multiple images. It would be nice to have the text
centered vertically also, but I'm not clear on how to do that.
import Image, random, textwrap, ImageFont, ImageDraw, os, sys
basepath = os.path.dirname(sys.argv[0]) + "/"
for n in xrange(10):
keywordlist = []
imglist = []
keyword = file(basepath + "text.txt", "r")
for line in keyword:
keywordlist.append(line.replace("\n", ""))
def type(name):
value = name[random.randint(0,len(name)-1)]
return value
def random_color():
return (random.randint(0,155), random.randint(0,155), random.randint(0,155))
astr = ('%s' %(type(keywordlist)))
para = textwrap.wrap(astr,width=19)
MAX_W,MAX_H=640,400
im = Image.new('RGB', (MAX_W, MAX_H), (random_color()))
draw = ImageDraw.Draw(im)
font = ImageFont.truetype('C:/windows/fonts/Arialbd.ttf', 58)
current_h=0
for line in para:
w,h=draw.textsize(line, font=font)
draw.text(((MAX_W-w)/2, current_h), line, font=font,)
current_h+=h
im.save('img%000d.jpg' % n)
Here is a sample of the output:
Answer: Use [the `blend`
function](http://www.pythonware.com/library/pil/handbook/image.htm#image-
blend-function):
new_image = Image.blend(solid_color_image, picture, 0.2)
|
Google App Engine aborts on missing environment variable DJANGO_SETTINGS_MODULE
Question: This is a follow-up question for [Google App Engine and Django
support](http://stackoverflow.com/questions/14137404/google-app-engine-and-
django-support):
The tutorial works great for an empty project, however when I try to deploy an
existing Django app to Google App Engine, it starts throwing errors:
Traceback (most recent call last):
File "/python27_runtime/python27_lib/versions/1/google/appengine/runtime/wsgi.py", line 223, in Handle
result = handler(dict(self._environ), self._StartResponse)
File "/python27_runtime/python27_lib/versions/third_party/django-1.4/django/core/handlers/wsgi.py", line 219, in __call__
self.load_middleware()
File "/python27_runtime/python27_lib/versions/third_party/django-1.4/django/core/handlers/base.py", line 39, in load_middleware
for middleware_path in settings.MIDDLEWARE_CLASSES:
File "/python27_runtime/python27_lib/versions/third_party/django-1.4/django/utils/functional.py", line 184, in inner
self._setup()
File "/python27_runtime/python27_lib/versions/third_party/django-1.4/django/conf/__init__.py", line 40, in _setup
raise ImportError("Settings cannot be imported, because environment variable %s is undefined." % ENVIRONMENT_VARIABLE)
ImportError: Settings cannot be imported, because environment variable DJANGO_SETTINGS_MODULE is undefined.
And a second, which might be related:
Traceback (most recent call last):
File "/python27_runtime/python27_lib/versions/1/google/appengine/runtime/wsgi.py", line 223, in Handle
result = handler(dict(self._environ), self._StartResponse)
File "/python27_runtime/python27_lib/versions/third_party/django-1.4/django/core/handlers/wsgi.py", line 219, in __call__
self.load_middleware()
File "/python27_runtime/python27_lib/versions/third_party/django-1.4/django/core/handlers/base.py", line 39, in load_middleware
for middleware_path in settings.MIDDLEWARE_CLASSES:
File "/python27_runtime/python27_lib/versions/third_party/django-1.4/django/utils/functional.py", line 184, in inner
self._setup()
File "/python27_runtime/python27_lib/versions/third_party/django-1.4/django/conf/__init__.py", line 42, in _setup
self._wrapped = Settings(settings_module)
File "/python27_runtime/python27_lib/versions/third_party/django-1.4/django/conf/__init__.py", line 95, in __init__
raise ImportError("Could not import settings '%s' (Is it on sys.path?): %s" % (self.SETTINGS_MODULE, e))
ImportError: Could not import settings 'settings' (Is it on sys.path?): No module named settings
I have modified my settings.py as per the tutorial. The app deploys without
problems and the syncdb works as well; the database and all required tables
are in place.
I found [this
reference](https://groups.google.com/forum/?fromgroups=#!topic/google-
appengine/lJorqc0p3MA) to the error message as shown in the log but its
suggested fix did not help.
Any ideas what might be causing this?
**EDIT:**
To shorten this already lengthy question I removed the previously posted
`wsgi.py` file. I had nothing to do with this issue.
**EDIT 2:**
I think I made a small improvement and GAE is now complaining:
ImportError: No module named properties
I presume there might be an entry missing in my app.yaml file but I have no
clue as to which file that may be. I found some references regarding missing
modules but none that reflect this error message...
Answer: After much trial and error I managed to solve this, albeit partially:
I did not manage to get my existing `PyCharm` project deployed (yet). As I was
keen to have a version running on GAE I went for a different approach and
created a new empty Django project (`project 2`) on my local machine.
I first deployed the blank project using [this
tutorial](http://howto.pui.ch/post/39245389801/tutorial-django-on-appengine-
using-google-cloud-sql) which ran fine. I then copied my `models.py` file from
my existing PyCharm project to `project 2` and added an app called
`properties` which uses the `models.py` file. Initially this went wrong as GAE
kept complaining it could not find my `properties` app. After fiddling about
with it, it suddenly appeared in my admin. I'm not sure what caused the
initial problem but it's working now.
Things crucial to success for me:
I added the following to the very top of my settings.py:
import os
ROOT_PATH = os.path.dirname(__file__)
... and then replaced the default `STATIC_ROOT` with:
STATIC_ROOT = ROOT_PATH + os.sep + 'static'
Then I ran:
python manage.py collectstatic
from the dir of `project 2`. This collects the required static files which
Django admin uses (image files, css files etc)
So, I currently have a stripped down version of my original project running on
GAE. Things that are missing:
* The original project used `grappelli` for a more styled admin interface. I'm not sure whether this will run on GAE. **EDIT: Deploying Grappelli on GAE is reasonbly easy. Just copy the Grappelli package to your project dir and run`manage.py collectstatic`. Also add grappelli urls as per documention. Redeploy. Done.**
* The original project uses a module called `templated_email` to send out templated emails from my `properties` app. Same as `grappelli`: I'm not sure whether this is supported by GAE. Hopefully it will run on GAE as it is crucial for my specific app. **EDIT: I bumped into[this](http://venodesigns.net/2010/07/13/rendering-emails-from-django-templates/) little gem which makes templated_email obsolete and lets me plug into GAE mail system.**
To be honest, this approach partially defies the benefits of PyCharm which
should fully support Django and GAE out of the box. It will probably require
some additional research and tweaking to get that up and running.
Any comments or insights re the above are obviously appreciated!
|
python topN max heap, use heapq or self implement?
Question: there's heapq in python, for general usage. i want recording topN(0~20) for
10e7 records.
if use heapq, should use '-' to translate max to min; and recording a min
number of bottom, to call heapq.heappushpop()
should i use heapq or self implement a heap(maybe buggy or less efficient)?
#update
import heapq
class TopN(object):
"""
v format: (num, value)
after looking into http://hg.python.org/cpython/file/2.7/Lib/heapq.py,
i find heappushpop already optimize, no need bottom value
feed() can be optimize further, if needed:
using func object instead of compare len(self.h) each time
"""
def __init__(self, N):
self.N = N
self.h = []
def feed(self, v):
if len(self.h) < self.N:
heapq.heappush(self.h, v)
else:
heapq.heappushpop(self.h, v)
def result(self):
self.h.sort(reverse=True)
return self.h
def t_topn():
topn = TopN(10)
for i in xrange(5):
topn.feed((i, str(i)))
res = topn.result()
assert sorted(res, reverse=True) == res
def t_topn_random():
import random
topn = TopN(10)
for i in xrange(100):
x = random.randint(0, 1e4)
topn.feed((x, str(x)))
res = topn.result()
assert sorted(res, reverse=True) == res
if __name__ == '__main__':
t_topn()
t_topn_random()
Answer: The only problem with `heapq` is that it doesn't provide a `key` function like
everything else in the stdlib does. (If you're curious why, Raymond Hettinger
explains in [this email](http://code.activestate.com/lists/python-
list/162387/). He's right that `heapq` couldn't provide the same interface as
other sort functions—but the reasons don't affect your use case, where `key`
would just be `lambda x: -x`.)
The usual workaround is to decorate-heap-undecorate. That is, put a modified
version of your values into the heap that sorts by `key`. Normally, this means
one of the following:
* Storing `key(x)` instead of `x`, and then accessing `unkey(value)` instead of `value` (assuming `key` is reversible).
* Storing `(key(x), x)` instead of `x`, and then accessing `value[1]`. (This can break stability, but `heapq` doesn't promise stability anyway.)
* Writing a wrapper class that implements a custom `__le__` method, then storing `Wrapper(x)` instead of `x` and accessing `value.value` instead of `value`.
In your case, the key function is reversible. So, just store `-x`, and access
`-value`. That's about as trivial as decoration gets.
Still, regardless of how simple it is, you should probably write a wrapper, or
you will screw it up at some point. For example, you could write a `maxheap`
that wraps the minheap in `heapq` like this:
import heapq
def heapify(x):
for i in range(len(x)):
x[i] = -x[i]
heapq.heapify(x)
def heappush(heap, item):
heapq.heappush(heap, -item)
def heappop(heap):
return -heapq.heappop(heap)
… and so on for any other functions you need. It may be a bit of a pain, but
it's a lot less work than implementing the whole thing from scratch.
While you're at it, you may want to wrap the heap in an object-oriented API so
you can do `heap.push(x)` instead of `heapq.heappush(heap, x)`, etc.
import heapq
class MaxHeap(object):
def __init__(self, x):
self.heap = [-e for e in x]
heapq.heapify(self.heap)
def push(self, value):
heapq.heappush(self.heap, -value)
def pop(self):
return -heapq.heappop(self.heap)
…
If you take a quick look around the recipes at ActiveState or the modules on
PyPI, you should find that others have already done most of the work for you.
Alternatively, you could copy and paste the `heapq` source (it's pure Python)
as `maxheapq.py` and just replace the `cmp_lt` function with its opposite. (Of
course if you're doing that, it's probably just as easy, and certainly a lot
clearer, to modify `cmp_lt` to take a `key` argument in the first place, and
modify all the other functions to pass the `key` through—bearing in mind that
it won't be as generally applicable anymore, because it can't make the usual
guarantee that `key` is only called once.)
If you really want to live dangerously (you shouldn't), you could even
monkeypatch it:
import heapq
def cmp_gt(x, y):
return y < x if hasattr(y, '__lt__') else not (x <= y)
heapq.cmp_lt = cmp_gt
But you don't want to do that in real code.
|
Python QueryFrame returns None, but C++ bindings work
Question: In OpenCV 2.3.1 (built from source) on Ubuntu 10.04, the C++ fragment
cvNamedWindow("Camera", 1);
CvCapture* capture = cvCaptureFromCAM(CV_CAP_ANY);
while (1) {
IplImage* frame = cvQueryFrame(capture);
cvShowImage("Camera", frame);
key = cvWaitKey(10);
...
will open up a window and show video from my ThinkPad camera, but
import cv2.cv as cv
# or import cv
cv.NamedWindow("Camera", 1)
capture = cv.CaptureFromCAM(-1)
while True:
frame = cv.QueryFrame(capture)
cv.ShowImage("Camera", frame)
key = cv.WaitKey(10)
...
fails (the window is gray), because `cv.QueryFrame` returns `None` (and the
light on the laptop camera doesn't come on.)
Any idea what may be going on here (and how I might remedy it)?
`cv.QueryFrame` works when displaying `.jpg`, so this seems to be a camera
issue.
Answer: Found a workaround, via [opencv+python+linux+webcam = cannot capture
frames](http://stackoverflow.com/questions/12717743/opencvpythonlinuxwebcam-
cannot-capture-frames), which I'll leave here for posterity.
Install `lib4vl` (`apt-get install libv4l-dev`) and in the `cmake` step of
building `OpenCV`, pass `-D WITH_4VL=ON`. (I'd been building with that OFF.)
Why C++ works without `lib4vl` but the Python bindings require it to work with
a webcam is a puzzle, which perhaps some OpenCV-knowledgable person can
explain. I'd love to hear an explanation.
|
Outlining a Solution Stack
Question: please excuse my ignorance as I'm an Aerospace Engineer going headfirst into
the software world.
I'm building a web solution that allows small computers (think beagleboard) to
connect to a server that sends and receives data to these clients. The
connection will be over many types including GPRS/3G/4G.
The user will interact with clients in real time through webpages served by
this central server. The solution must scale well.
I've been using python for the client side and some simple ruby code for the
servers with Heroku. I have also tried a bit of NodeJS and Ruby on Rails. With
so many options i'm struggling to see the forest from the trees and wondering
where these languages will fit into my stack.
Your help is appreciated; I'm happy to give more details.
Answer: It all depends on what you are actually trying to do and what your
requirements are.
There is no real "right" language for things like these, it's mostly
determined by the Frameworks you'll be using on those language (since all are
general-purpose programming languages) and your personal
preference/experience.
I can't comment too much on Python as I never tried it really, but from what I
heard/saw it can be used for all things Ruby is also used, although the
Community around Python is a bit smaller with Python being used a lot more in
the Scientific community (that may be good if your app may be doing any crayz
calculations).
That leads us to Ruby. Ruby and the Ruby on Rails framework is mostly used to
write Web-Applications and Services. Ruby is a very elegant language to
program in and the tools are very mature and easy to work with. Rails is a
framework on Ruby that makes Web-Development very simple in providing you with
a very good set of tools especially suited to write data-driven web-apps. Very
flexible and a joy to work with. There are however some drawbacks to Ruby at
the moment, mostly related to poor threading.
Node.JS is a new language that is focused on paralellism and supports all
things Ruby and Python can do, although it's documentation is lacking compared
to what Ruby will give you. It's also not the most beginner-friendly choice as
JavaScript with all it's quirks and the callback-oriented async model is not
of the simplest thing around.
That said, Node is very bare metal and makes it very very easy to write
arbitrary TCP/UDP Servers that don't necessary work over HTTP. Custom
streaming protocols or any custom protocol in fact are almost trivially done
in Node.. (I don't advise you do that, but maybe that's important to your
task).
To be fair there are frameworks that facilitate writing of Web-Apps for node,
but the coices are a) not as mature as Rails or Django, and b) you have to
pick your framework choices.
This means: Where Rails does come with a lot of defaults that guide you,
(Rails for example has a default Database stack it's optimized around), Node
with Frameworks like Express only provide you with a bare-bones HTTP server
where you have to bring in the Database of your choice etc...
In closing: All languages and frameworks you asked about are mostly used for
writing Web-Applications. They all can however be used to write a client that
consumes the service too - it mostly comes down to general preference.
|
python:Import module from memory
Question: > **Possible Duplicate:**
> [How to load compiled python modules from
> memory?](http://stackoverflow.com/questions/1830727/how-to-load-compiled-
> python-modules-from-memory)
I have some python file in the memory that may be StringIO.I how to import
module file stored in the memory.I do not want to save it to disk and then
load.
It look like:
import StringIO.StrngIO([buf])
Answer: A nice approach is to use custom Meta import hooks as described in [PEP
302](http://www.python.org/dev/peps/pep-0302/#specification-
part-2-registering-hooks). One can write a class that imports modules
dynamically from a dictionary of strings:
"""Use custom meta hook to import modules available as strings.
Cp. PEP 302 http://www.python.org/dev/peps/pep-0302/#specification-part-2-registering-hooks"""
import sys
import imp
modules = {"a" :
"""def hello():
return 'Hello World A!'""",
"b":
"""def hello():
return 'Hello World B!'"""}
class StringImporter(object):
def __init__(self, modules):
self._modules = dict(modules)
def find_module(self, fullname, path):
if fullname in self._modules.keys():
return self
return None
def load_module(self, fullname):
if not fullname in self._modules.keys():
raise ImportError(fullname)
new_module = imp.new_module(fullname)
exec self._modules[fullname] in new_module.__dict__
return new_module
if __name__ == '__main__':
sys.meta_path.append(StringImporter(modules))
# Let's use our import hook
from a import hello
print hello()
from b import hello
print hello()
BTW: If you don't want that much and just want to import one string, then
stick to the implementation of the method load_module. All you need is inside
it.
|
python Channel API expiry and usage in google app engine
Question: I want to use the channel api to push updates to open pages, What I have done
so far is to store the page client ids in ndb - I have included a code summary
My question is: How do I manage closed pages and expired tokens?
and is this the best way to push updates to many open pages?
open page code:
import webapp2
import uuid
from google.appengine.api import channel
from google.appengine.ext import ndb
class Frame(ndb.Model):
clientID = ndb.StringProperty()
date = ndb.DateTimeProperty(auto_now_add=True)
class MainHandler(BaseHandler):
def get(self):
client_id = str(uuid.uuid4())
channel_token = channel.create_channel(client_id)
frame = Frame(clientID = client_id)
frame.put()
self.render_response('home.html',** "token":channel_token,"client_id":client_id)
send message code:
from google.appengine.api import channel
from google.appengine.ext import ndb
class Frame(ndb.Model):
clientID = ndb.StringProperty()
date = ndb.DateTimeProperty(auto_now_add=True)
frames = Frame.query().fetch(10)
for i in frames:
channel.send_message(i.clientID, "some message to update")
Answer: When you enable channel_presence, your application receives POSTs to the
following URL paths:
POSTs to /_ah/channel/connected/
POSTs to /_ah/channel/disconnected/
These signal that the client has connected to the channel and can receive
messages or has dicsonnected.
[Tracking_Client_Connections_and_Disconnections](https://developers.google.com/appengine/docs/python/channel/overview#Tracking_Client_Connections_and_Disconnections)
Dealing with expired tokens:
> By default, tokens expire in two hours, unless you explicitly set an
> expiration time by providing the duration_minutes argument to the
> create_channel() function when generating the token. If a client remains
> connected to a channel for longer than the token duration, the socket’s
> onerror() and onclose() callbacks are called. At this point, the client can
> make an XHR request to the application to request a new token and open a new
> channel.
So on your `onerror` function you basically do it all over again just like the
original connection.
[Tokens and
security](https://developers.google.com/appengine/docs/python/channel/overview#Tokens_and_Security)
To send updates to many open pages simply iterate round your list of connected
users and send them the message individually. There is no "transmit to all"
functionality.
You may also want to build in a "heartbeat" that sends messages to supposedly
connected clients and remove them if no reply. This is because sometimes
(apparently) the disconnected messages are not sent (power failure, whatever)
when the browser window is closed.
|
How to handle download pop up window using Python and get the file saved?
Question: I have a link, which contains downloadble file,now when i am putting that link
onto the browser, and hit `ENTER` a popup window is coming to download. Now
using Python can we save that file in local machine?
say downloadable link :
https://xyz.test.com/aems/file/filegetrevision.do?fileEntityId=8120070&cs=LU31NT9us5P9Pvkb1BrtdwaCrEraskiCJcY6E2ucP5s.xyz
**Code**
it is for preparing the link: but finally i couldn't find a way how to handle
this:
for a in soup.find_all('a', {"style": "display:inline; position:relative;"}, href=True):
href = a['href'].strip()
href = "https://xyz.test.com/" + href
print(href)
[Download window](http://i.stack.imgur.com/5nIcZ.png)
Answer: If your intention is not to test the _download popup_ itself, but the
existence/content of the file, you can download it using urllib:
import urllib
urllib.urlretrieve(href, filename)
You would need to add the necesary exception handling (to make sure the URL
really points to something) and the file processing once downloaded to verify
it's content.
|
exit on KeyboardInterrupt after generating plots in while loop
Question: I am monitoring an experiment in real time using matplotlib to generate plots
in a while loop. Ideally, the loop should exit on something like a
`KeyboardInterrupt`. This works well enough in an Ubuntu test. In Windows 7,
using `ipython`, it exits with `"Terminate batch job (Y/N)?"` then closes the
interpreter. I would like to avoid this behavior and leave the interpreter
open after the KeyboardInterrupt. Here is a test script.
[EDIT 2]: This script works fine in Windows if `ipython` is loaded as `ipython
--pylab`.
import time
import numpy as np
import matplotlib.pyplot as plt
fig = plt.figure()
ax = fig.add_subplot(111)
line, = ax.plot([0], [0], 'b-o')
window = 50
plot_data = np.zeros((window, 2))
i = 0
start = time.time()
while True:
try:
data = [time.time() - start, np.random.rand()]
print ' '.join('{:.2f}'.format(x) for x in data)
if i < window:
plot_data[i,:] = data
line.set_data(plot_data[0:i+1,0], plot_data[0:i+1,1])
else:
plot_data[0:window-1] = plot_data[1:window]
plot_data[window-1] = data
line.set_data(plot_data[:,0], plot_data[:,1])
ax.relim()
ax.autoscale_view(True,True,True)
fig.canvas.draw()
plt.pause(0.1)
i += 1
except KeyboardInterrupt:
print "Program ended by user.\n"
break
print 'Success!'
[EDIT 1]: I should be more clear why I tagged this with matplotlib. The below
example script executes with no problems in either operating system.
i = 0
start = time.time()
while True:
try:
data = [time.time() - start, np.random.rand()]
print ' '.join('{:.2f}'.format(x) for x in data)
time.sleep(0.1)
except KeyboardInterrupt:
print "Proram ended by user. \n"
break
print 'Success!'
All of the packages were installed yesterday as part of a clean installation
of `Enthought`.
Answer: Right now the best way I've found to solve this problem across several Windows
machines is as follows...
print 'press \'q\' to end run'
time.sleep(1.0)
fig = plt.figure()
ax = fig.add_subplot(111)
line, = ax.plot([0], [0], 'b-o')
window = 150
plot_data = np.zeros((window, 2))
i = 0
start = time.time()
while True:
data = [time.time() - start, np.random.rand()]
print ' '.join('{:.2f}'.format(x) for x in data)
if i < window:
plot_data[i,:] = data
line.set_data(plot_data[0:i+1,0], plot_data[0:i+1,1])
else:
plot_data[0:window-1] = plot_data[1:window]
plot_data[window-1] = data
line.set_data(plot_data[:,0], plot_data[:,1])
ax.relim()
ax.autoscale_view(True,True,True)
fig.canvas.draw()
plt.pause(delay)
i += 1
if msvcrt.kbhit():
if ord(msvcrt.getch()) == 113:
print "Program ended by user.\n"
break
print 'Success!'
Unfortunately, this is not at all platform independent, but everything I've
read over the past few days leads me to believe that platform-independent
keyboard input is not really achievable. The code in my original question
works well in Unix and some Windows installations. This code works well in the
few Windows installations I've tried. All of this works best when run through
`ipython --pylab`. This might have to be good enough for now.
|
Impossible to initialize Elixir
Question: I'm starting with Elixir and SQL Alchemy. I've created a python file
connecting with a Mysql database to but as soon as I execute with python I get
the error bellow:
root@raspberrypi:/Python/mainFlask/yonkiPOPS# python yonki.py
Traceback (most recent call last):
File "yonki.py", line 1, in <module>
from elixir import metadata, Entity, Field
File "/usr/local/lib/python2.7/dist-packages/Elixir-0.7.1-py2.7.egg/elixir/__init__.py", line 29, in <module>
from elixir.entity import Entity, EntityBase, EntityMeta, EntityDescriptor, \
File "/usr/local/lib/python2.7/dist-packages/Elixir-0.7.1-py2.7.egg/elixir/entity.py", line 17, in <module>
from sqlalchemy.orm import MapperExtension, mapper, object_session, \
ImportError: cannot import name ScopedSession
I have been looking for it but I don't find the reason. This is the yonki.py
file:
from elixir import metadata, Entity, Field
from elixir import Unicode, UnicodeText
from elixir import *
class User(Entity):
username = Field(String(64))
metadata.bind = 'mysql://root:nomasandroid42@localhost/yonkiPOPS'
session.bind.echo = True
setup_all()
create_all()
I think that it's maybe due to a required module not installed but I don't
know which one.
Answer: Elixir 0.7.1 seems to be incompatible with the latest version of SQLalchemy,
0.8. You can solve that problem with
sudo pip install SQLAlchemy==0.7.8
|
Python BeautifulSoup get text from HTML
Question: I have some HTML code like this:
<p>aaa</p>bbb
<p>ccc</p>ddd
How can I get 'bbb' and 'ddd'?
Answer: You can read the subsequent sibling of each `p` tag (note this is very
specific to this text, so hopefully it can be expanded to your situation):
In [1]: from bs4 import BeautifulSoup
In [2]: html = """\
...: <p>aaa</p>bbb
...: <p>ccc</p>ddd"""
In [3]: soup = BeautifulSoup(html)
In [4]: [p.next_sibling for p in soup.findAll('p')]
Out[4]: [u'bbb\n', u'ddd']
This picks up the trailing newline, so you can strip it off if need be:
In [5]: [p.next_sibling.strip() for p in soup.findAll('p')]
Out[5]: [u'bbb', u'ddd']
The general idea is that you locate the tag(s) before your target text and
then find the next sibling element, which should be your text.
|
Deep version of sys.getsizeof
Question: I want to calculate the memory used by an object. `sys.getsizeof` is great,
but is shallow (for example, called on a list, it would not include the memory
taken by the list's elements).
I'd like to write a generic "deep" version of `sys.getsizeof`. I understand
there is some ambiguity in the definition of "deep"; I'm perfectly happy with
the [definition followed by
`copy.deepcopy`](http://docs.python.org/3.4/library/copy.html).
Here's my first attempt:
def get_deep_sizeof(x, level=0, processed=None):
if processed is None:
# we're here only if this function is called by client code, not recursively
processed = set()
processed.add(id(x))
mem = sys.getsizeof(x)
if isinstance(x, collections.Iterable) and not isinstance(x, str):
for xx in x:
if id(xx) in processed:
continue
mem += get_deep_sizeof(xx, level+1, processed)
if isinstance(x, dict):
mem += get_deep_sizeof(x[xx], level+1, processed)
return mem
It suffers from two known problems, and an unknown number of unknown problems:
* I don't know how to traverse a generic container in a way that captures all the linked objects. Therefore, I iterated using `in`, and hard coded the case of dictionary (to include values, and not just the keys). Obviously, this will not work for other classes like dictionary.
* I had to hard code the exclusion of `str` (which is an iterable, and yet does not have links to any other objects). Again, this will break if there are more objects like that.
I suspect that using `in` is not a good idea, but I'm not sure what else to
do.
Answer: I think that [Pympler](http://packages.python.org/Pympler/) has already beaten
you to the punch on this one.
From their documentation:
>>> from pympler.asizeof import asizeof
>>> obj = [1, 2, (3, 4), 'text']
>>> asizeof(obj)
176
If you want a specific example, you can find the source for `asizeof`
[here](http://code.google.com/p/pympler/source/browse/trunk/pympler/asizeof.py).
|
Simply a try/except with lambda - Python?
Question: Is there a way to simplify this try/except into a one line with lambda?
alist = ['foo','bar','duh']
for j,i in enumerate(alist):
try:
iplus1 = i+alist[j+1]
except IndexError:
iplus1 = ""
Is there other way other than:
j = '' if IndexError else trg[pos]
Answer: No, Python doesn't have any shorthands or simplifications to the
`try`/`except` syntax.
To solve your specific problem, I would probably use something like:
for j, i in enumerate(alist[:-1]):
iplus1 = i + alist[j + 1]
Which would avoid the need for an exception.
Or to get super cool and generic:
from itertools import islice
for j, i in enumerate(islice(alist, -1)):
iplus1 = i + alist[j + 1]
Alternative, you could use: `itertools.iziplongest` to do something similar:
for i, x in itertools.izip_longest(alist, alist[1:], fillvalue=None):
iplus1 = i + x if x is not None else ""
Finally, one small note on nomenclature: `i` is traditionally used to mean
"index", so using `for i, j in enumerate(…)` would be more "normal".
|
Minimal HTTP server with Werkzeug - Internal Server Error
Question: To demonstrate basics HTTP handling, I'm in the process of trying to define a
really minimal HTTP server demonstration. I have been using the excellent
[werkzeug](http://werkzeug.pocoo.org/) library that I'm trying to "dumb" down
a bit more. My current server does too much :)
#!/usr/bin/env python2.7
# encoding: utf-8
if __name__ == '__main__':
from werkzeug.serving import run_simple
run_simple('127.0.0.1', 6969, application=None)
`run_simple` is handling already too many things. When making a request for
this server,
→ http GET http://127.0.0.1:6969/
we get:
HTTP/1.0 500 INTERNAL SERVER ERROR
Content-Type: text/html
Content-Length: 291
Server: Werkzeug/0.8.3 Python/2.7.1
Date: Tue, 08 Jan 2013 07:45:46 GMT
<!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 3.2 Final//EN">
<title>500 Internal Server Error</title>
<h1>Internal Server Error</h1>
<p>The server encountered an internal error and was
unable to complete your request. Either the server
is overloaded or there is an error in the application.</p>
I would love to reduce it to the bare minimum. And use the 500 Internal Server
Error as a catch all. Ideally the Response from the server should be 500 for
any HTTP requests and just that, because the server doesn't know anything
about the requests
HTTP/1.0 500 INTERNAL SERVER ERROR
Then in a second stage I will probably add
HTTP/1.0 500 INTERNAL SERVER ERROR
Content-Type: text/plain
Internal Server Error
Then start to handle requests by understanding them. The goal is to be
educative in the process. Any suggestions for taking over the default answers
is welcome.
**Update 001**
with:
#!/usr/bin/env python2.7
# encoding: utf-8
from werkzeug.wrappers import BaseResponse as Response
def application(environ, start_response):
response = Response('Internal Server Error', status=500)
return response(environ, start_response)
if __name__ == '__main__':
from werkzeug.serving import run_simple
run_simple('127.0.0.1', 6969, application)
It will return
HTTP/1.0 500 INTERNAL SERVER ERROR
Content-Type: text/plain; charset=utf-8
Content-Length: 21
Server: Werkzeug/0.8.3 Python/2.7.1
Date: Tue, 08 Jan 2013 07:55:10 GMT
Internal Server Error
I want to remove at least the server and the date which are optional.
Answer: As basic example, I wouldn't use a third-party library. You can use the
BaseHTTPServer-module that comes with Python.
import BaseHTTPServer
PORT = 8000
class MyHandler(BaseHTTPServer.BaseHTTPRequestHandler):
def send_response(self, code, message=None):
"""Send the response header and log the response code.
In contrast to base class, do not send two standard headers
with the server software version and the current date.
"""
self.log_request(code)
if message is None:
if code in self.responses:
message = self.responses[code][0]
else:
message = ''
if self.request_version != 'HTTP/0.9':
self.wfile.write("%s %d %s\r\n" %
(self.protocol_version, code, message))
def do_GET(self):
self.send_response(500)
self.send_header("Content-type", "text/html")
self.end_headers()
self.wfile.write("Internal Server Error\n")
httpd = BaseHTTPServer.HTTPServer(("", PORT), MyHandler)
print "serving at port", PORT
httpd.serve_forever()
This will give us the following response:
HTTP/1.0 500 Internal Server Error
Content-type: text/html
Internal Server Error
The place where you can do all your changes now is in the do_GET-method. I
think it is quite obvious what each line does.
**Alternative 1:**
Even more basic is
import SocketServer
response = """HTTP/1.0 500 Internal Server Error
Content-type: text/html
Invalid Server Error"""
class MyTCPHandler(SocketServer.BaseRequestHandler):
"""
The RequestHandler class for our server.
It is instantiated once per connection to the server, and must
override the handle() method to implement communication to the
client.
"""
def handle(self):
# self.request is the TCP socket connected to the client
self.data = self.request.recv(1024).strip()
self.request.sendall(response)
if __name__ == "__main__":
HOST, PORT = "localhost", 8000
server = SocketServer.TCPServer((HOST, PORT), MyTCPHandler)
server.serve_forever()
|
Automatically cropping an image with python/PIL
Question: Can anyone help me figure out what's happening in my image auto-cropping
script? I have a png image with a large transparent area/space. I would like
to be able to automatically crop that space out and leave the essentials.
Original image has a squared canvas, optimally it would be rectangular,
encapsulating just the molecule.
here's the original image: 
Doing some googling i came across PIL/python code that was reported to work,
however in my hands, running the code below over-crops the image.
import Image
import sys
image=Image.open('L_2d.png')
image.load()
imageSize = image.size
imageBox = image.getbbox()
imageComponents = image.split()
rgbImage = Image.new("RGB", imageSize, (0,0,0))
rgbImage.paste(image, mask=imageComponents[3])
croppedBox = rgbImage.getbbox()
print imageBox
print croppedBox
if imageBox != croppedBox:
cropped=image.crop(croppedBox)
print 'L_2d.png:', "Size:", imageSize, "New Size:",croppedBox
cropped.save('L_2d_cropped.png')
the output is this:
Can anyone more familiar with image-processing/PLI can help me figure out the
issue?
Answer: For me it works as:
import Image
import sys
image=Image.open('L_2d.png')
image.load()
imageSize = image.size
imageBox = image.getbbox()
cropped=image.crop(imageBox)
cropped.save('L_2d_cropped.png')
When you search for boundaries by `mask=imageComponents[3]`, you search only
by blue channel.
|
Prevent OS X from going to sleep with Python?
Question: Is there a way to prevent a computer running OS X from going to sleep from
within a Python script?
Answer: You can call the **caffeinate** command.
subprocess.Popen('caffeinate')
This is how I use it:
import sys
import subprocess
if 'darwin' in sys.platform:
print('Running \'caffeinate\' on MacOSX to prevent the system from sleeping')
subprocess.Popen('caffeinate')
|
Force importing module from current directory
Question: I have package `p` that has modules `a` and `b`. `a` relies on `b`:
`b.py` contents:
import a
However I want to _ensure_ that `b` imports my `a` module from the same `p`
package directory and not just any `a` module from `PYTHONPATH`.
So I'm trying to change `b.py` like the following:
from . import a
This works as long as I import `b` when I'm outside of `p` package directory.
Given the following files:
/tmp
/p
a.py
b.py
__init__.py
The following works:
$ cd /tmp
$ echo 'import p.b' | python
**The following does NOT work:**
$ cd /tmp/p
$ echo 'import b' | python
Traceback (most recent call last):
File "<stdin>", line 1, in <module>
File "b.py", line 1, in <module>
from . import a
ValueError: Attempted relative import in non-package
**Why?**
P.S. I'm using Python 2.7.3
Answer: After rereading the Python [import
documentation](http://docs.python.org/2/tutorial/modules.html#intra-package-
references), the correct answer to my original problem is:
_To ensure that`b` imports `a` from its own package its just enough to write
the following in the `b`:_
import a
Here is the quote from the docs:
> The submodules often need to refer to each other. For example, the surround
> module might use the echo module. In fact, **such references are so common
> that the import statement first looks in the containing package before
> looking in the standard module search path.**
**Note:** As J.F. Sebastian suggest in the comment below, use of implicit
imports is not advised, and they are, in fact, gone in Python 3.
|
python network file writing in a robust manner
Question: I am looking for a robust way to write out to a network drive. I am stuck with
WinXP writing to a share on a Win2003 server. I want to pause writing if the
network share goes down... then reconnect and continue writing once the
network resource is available. With my initial code below, what happens is the
'except' catches the IOError when the drive goes away, but then when the drive
becomes available again, the outf operations continue to IOError.
import serial
with serial.Serial('COM8',9600,timeout=5) as port, open('m:\\file.txt','ab') as outf:
while True:
x = port.readline() # read one line from serial port
if x: # if the there was some data
print x[0:-1] # display the line without extra CR
try:
outf.write(x) # write the line to the output file
outf.flush() # actually write the file
except IOError: # catch an io error
print 'there was an io error'
Answer: I suspect that once an open file goes into an error state because of the
IOError that you will need to reopen it. You could try something like this:
with serial.Serial('COM8',9600,timeout=5) as port:
while True:
try:
with open('m:\\file.txt','ab') as outf:
while True:
x = port.readline() # read one line from serial port
if x: # if the there was some data
print x[0:-1] # display the line without extra CR
try:
outf.write(x) # write the line to the output file
outf.flush() # actually write the file
break
except IOError:
print 'there was an io error'
This puts the exception handling inside an outer loop that will reopen the
file (and continue reading from the port) in the event of an exception. In
practice you would probably want to add a `time.sleep()` or something to the
`except` block in order to prevent the code from spinning.
|
Why is 'import simplejson' failing in Python 2.7.3 code, but not in the interpreter?
Question: There are two instances running uwgsi and nginx servers. Each hosts a Flask
application. Both are running on a Python 2.7.3 path. One of the servers
throws an ImportError for the "import simplejson" statement. The interpreter
on both servers will accept this import statement without complaint.
Here's the source of application A:
1 from flask import Flask, request, session, g, redirect, url_for, abort, render_template, flash, views
2 import sys
3 print sys.version
4 print sys.path
5
6 import os
7 import functools
8 import urllib,urllib2
9 import simplejson
10 from datetime import datetime, timedelta
And the source of application B:
1 from flask import Flask, request, session, g, redirect, url_for, abort, render_template, flash, views
2
3 import sys
4 print sys.version
5 print sys.path
6
7 import simplejson
8
9 import functools
Here's the sys.version and sys.path log output of server A:
2.7.3 (default, Aug 1 2012, 05:25:23)
[GCC 4.6.3]
['/srv/www/A/env/local/lib/python2.7/site-packages/setuptools-0.6c11-py2.7.egg',
'/srv/www/A/env/local/lib/python2.7/site-packages/pip-1.2.1-py2.7.egg',
'/srv/www/A/env/lib/python2.7/site-packages/setuptools-0.6c11-py2.7.egg',
'/srv/www/A/env/lib/python2.7/site-packages/pip-1.2.1-py2.7.egg',
'/srv/www/A/env/lib/python2.7',
'/srv/www/A/20120910/src',
'/usr/lib/python2.7',
'/usr/lib/python2.7/plat-linux2',
'/usr/lib/python2.7/lib-tk',
'/usr/lib/python2.7/lib-old',
'/usr/lib/python2.7/lib-dynload',
'/srv/www/A/env/local/lib/python2.7/site-packages',
'/srv/www/A/env/lib/python2.7/site-packages']
WSGI app 0 (mountpoint='notimportant.com|') ready in 1 seconds on interpreter 0x1b20420 pid: 11069
Here's the sys.version and sys.path log output of server B:
2.7.3 (default, Aug 1 2012, 05:25:23)
[GCC 4.6.3]
['/srv/www/B/env/local/lib/python2.7/site-packages/setuptools-0.6c11-py2.7.egg',
'/srv/www/B/env/local/lib/python2.7/site-packages/pip-1.2.1-py2.7.egg',
'/srv/www/B/env/lib/python2.7/site-packages/setuptools-0.6c11-py2.7.egg',
'/srv/www/B/env/lib/python2.7/site-packages/pip-1.2.1-py2.7.egg',
'/srv/www/B/env/lib/python2.7',
'/srv/www/B/20130105/src',
'/usr/lib/python2.7',
'/usr/lib/python2.7/plat-linux2',
'/usr/lib/python2.7/lib-tk',
'/usr/lib/python2.7/lib-old',
'/usr/lib/python2.7/lib-dynload',
'/srv/www/B/env/local/lib/python2.7/site-packages',
'/srv/www/B/env/lib/python2.7/site-packages']
Traceback (most recent call last):
File "/srv/www/B/20130105/src/B.py", line 7, in <module>
import simplejson
ImportError: No module named simplejson
unable to load app 0 (mountpoint='notimportant.com|') (callable not found or import error)
Any constructive ideas will be appreciated.
Answer: `simplejson` is an external library; it is bundled with Python 2.6 and up as
the [`json` module](http://docs.python.org/2/library/json.html).
Just use `import json` instead of `import simplejson`, _or_ install
`simplejson` on server B too.
If you replace your `simplejson` import with `json`, remember to fix any
references in the file. Alternatively, import it like this:
try:
import simplejson
except ImportError:
import json as simplejson
and it'll use the stdlib `json` module, renamed, and all your references to
`simplejson` will continue to work.
|
can python be useful to open multiple tabs in a browser in one shot?
Question: I am looking for a faster way to do my task. i have 40000 file downloadable
urls. I would like to download them in local desktop is.now the thought is
currently what I am doing is placing the link on the browser and then download
them via a script.now what I am looking for is to place 10 urls in a chunk to
the address bar and get the 10 files to be downloaded at the same time.If it
possible hope overall time will be decreased.
Sorry I was late to give the code,here it is :
def _download_file(url, filename):
"""
Given a URL and a filename, this method will save a file locally to the»
destination_directory path.
"""
if not os.path.exists(destination_directory):
print 'Directory [%s] does not exist, Creating directory...' % destination_directory
os.makedirs(destination_directory)
try:
urllib.urlretrieve(url, os.path.join(destination_directory, filename))
print 'Downloading File [%s]' % (filename)
except:
print 'Error Downloading File [%s]' % (filename)
def _download_all(main_url):
"""
Given a URL list, this method will download each file in the destination
directory.
"""
url_list = _create_url_list(main_url)
for url in url_list:
_download_file(url, _get_file_name(url))
Thanks,
Answer: Why use a browser? This seems like an [XY
problem](http://meta.stackexchange.com/a/66378).
To download files, I'd use a library like [requests](http://docs.python-
requests.org/) (or make a system call to `wget`).
Something like this:
import requests
def download_file_from_url(url, file_save_path):
r = requests.get(url)
if r.ok: # checks if the download succeeded
with file(file_save_path, 'w') as f:
f.write(r.content)
return True
else:
return r.status_code
download_file_from_url('http://imgs.xkcd.com/comics/tech_support_cheat_sheet.png', 'new_image.png')
# will download image and save to current directory as 'new_image.png'
You first have to install requests using whatever python package manager you
prefer e.g., `pip install requests`. You can also get fancier; e.g.,
|
Expose a C++ global variable in Python
Question: I'm trying to access to a C++ global variable in my Python code, using Cython.
Let's say I have the following array in my C++ code:
// Project.cpp
int myArr[2] = { 0, 1 };
So, in Cython to define a pointer to _myArr_ :
cdef extern int * myArr_ptr
Does **myArr_ptr** really points to the C++ array? Or is just a random value?
Answer: OK, the problem is:
`Project.cpp` has a global `int *myArr;`, it's not listed in `Project.h`, and
you want to access it from Cython without importing `Project.cpp`.
In the comments, you say:
> I can't include Project.cpp because this file will try to include other
> files that were already included and will try to redefine many variables.
The way you described it, there might be an elementary error here. You
probably know these basic things, so please don't be insulted that I bring
them up, but I just want to be thorough:
First, if your header files don't have guards against multiple inclusion, fix
that, and then you don't need to worry about "I can't include `Project.cpp`
because this file will try to include other files that were already included
and will try to redefine many variables." (And if you don't have header files,
and you're just doing everything in .cpp files with explicit `extern`
statements all over the place, don't do that—it's a bad idea in C and C++,
well before you get to Cythonizing.)
Second, if your module is meant to interface to a .so/.dll/.dylib that
`Project.cpp` is part of, you shouldn't be building against the source to that
library, but to the installed interface. On the other hand, if your module is
meant to directly include the C++ code, then you _have_ to include
`Project.cpp`. If you use `extern` declarations to reference things that you
aren't going to link in, you're just going to get a linker error—or, if you're
unlucky, everything will build but then fail at runtime.
Third, if it isn't actually global, you can't access from outside of
`Project.cpp`—for reasons of scope, lifetime, or linkage, no other kind of
variable is usable in a separate implementation file.
Again, I assume you know all those basic things, and I just misread your
comment. There _is_ a real problem case where you need to wrap something with
a poorly-designed API that requires you to reach into the internals, and that
can be tricky sometimes, and you probably did run into such a thing, and I
just haven't figured out exactly how.
There are three basic solutions.
First, obviously, if you can build a proper native API, then wrapping that API
in Cython is trivial. And this is useful for other reasons, at the same time.
Sometimes, this would be too much time and effort—e.g., if the native library
wasn't designed to be driven externally, and is a mass of 10 years of legacy
maintenance, and the only reason you're ever going to have to wrap it is the
current Cython project, you may not want to clean it up. Or, if it's a
rapidly-changing library that you need to keep up to date with and don't have
source control over, forking it and trying to keep in sync can be a nightmare.
And so on. But if there's no such reason in your case, this is the right
answer. If you can just `cdef extern from "project.h"`, everything is easy.
You can do a simpler version of that by creating a "shim API" at the native
level, creating separate `.h` files with the appropriate extern, function, and
type declarations for the various, functions, and types you need to use from
the internals. Then, you can just `cdef extern from "project_extras.h"`.
Finally, you can always write explicit `cdef extern` statements for anything,
without telling Cython where any of it comes from. Cython will turn this into
the appropriate native externs in the generated code, and if you get
everything right, it will work. There are some downsides here—[the
docs](http://docs.cython.org/src/userguide/external_C_code.html#referencing-c-
header-files) explain all the advantages of `cdef extern from` that you'll be
giving up. The short version is, your Cython declarations have to exactly
match the native declarations; otherwise, instead of getting automatically
fixed up or raising a nice error at the Cython stage, you'll get an
inscrutable error message from the C compiler referring to the unreadable
Cython-generated C code instead of your actual code—or, worse, code that
compiles but does the wrong thing.
For the case of a simple `int *` or `int []` value, all of this scarcely
matters, because that doesn't need any interpretation; a plain `cdef extern`
should be just fine.
|
How to pass a parameter list to another function in Python?
Question: Using `optparse`, I want to separate the list of option list parameters from
the place where I call add_option(). How do I package the stuff up in File A
(and then unpack in file B) so that this will work? The
parser_options.append() lines will not work as written...
File A:
import file_b
parser_options = []
parser_options.append(('-b', '--bootcount', type='string', dest='bootcount', default='', help='Number of times to repeat booting and testing, if applicable'))
parser_options.append(('-d', '--duration', type='string', dest='duration', default='', help='Number of hours to run the test. Decimals OK'))
my_object = file_b.B(parser_options)
File B recieves parser_options as input:
import optparse
class B:
def __init__(self, parser_options):
self.parser = optparse.OptionParser('MyTest Options')
if parser_options:
for option in parser_options:
self.parser.add_option(option)
_*_ EDIT: Fixed to use ojbects
Answer: Rather than try to shoehorn your options into some data structure, wouldn't it
be simpler to define a function in file A that adds options to a parser you
give it?
File A:
def addOptions(parser):
parser.add_option('-b', '--bootcount', type='string', dest='bootcount', default='', help='Number of times to repeat booting and testing, if applicable')
parser.add_option('-d', '--duration', type='string', dest='duration', default='', help='Number of hours to run the test. Decimals OK')
File B:
import optparse
def build_parser(parser_options):
parser = optparse.OptionParser('MyTest Options')
if parser_options:
parser_options(parser)
elsewhere:
import file_a
import file_b
file_b.build_parser(file_a.addOptions)
|
Python @property in Flask configs?
Question: I'm currently learning Flask and I just set up a config file I load into the
app with:
app.config.from_object('myconfigmodule')
The config module has two classes in it, Config and DebugConfig and
DebugConfig inherits Config. I'd like to use @property getters to get config
variables rather than accessing them with `app.config['myvar']` because it
makes for cleaner code. I set this up and app.config does not see the
properties but I can still access the config class members with
`app.config['myvar']`
This is the error I get when I start my app:
Traceback (most recent call last):
File "runserver.py", line 3, in <module>
app.run(host=app.config['_APP_HOST'], debug=app.config.Debug)
AttributeError: 'Config' object has no attribute 'Debug'
In the config class the Debug property is as follows:
class Config (object):
_APP_DEBUG = False
@property
def Debug (self):
return self._APP_DEBUG
Am I doing something wrong here or does Flask just not like properties in
configs for some reason? Thanks for any help!
Answer: Flask has it's own `Config` class (a dict subclass) and it will pick out the
attributes of the object given to `from_object`, rather that using the given
object as is, as can be seen in the [source
code](https://github.com/mitsuhiko/flask/blob/master/flask/config.py#L163):
# class Config(dict):
# ...
for key in dir(obj):
if key.isupper():
self[key] = getattr(obj, key)
As you can see, it will only use _uppercase_ attributes.
Here's an example _by hand_ :
>>> from flask import config
>>> class X(object):
... REGULAR = True
... ignored = "not uppercase"
... def __init__(self):
... self.not_used = "because lowercase"
... self.OK = True
...
... @property
... def UPPER_PROP(self):
... return True
...
... @property
... def MIXED_case(self):
... return "wont work"
...
>>> x = X()
>>> c = config.Config(None)
>>> c.from_object(x)
>>> c
<Config {'REGULAR': True, 'OK': True, 'UPPER_PROP': True}>
That said, nothing will hold you back, if you want to implement something like
a [dot-dict'd](http://parand.com/say/index.php/2008/10/24/python-dot-notation-
dictionary-access/) subclass of flasks' `Config`. Whether the potential
confusion caused by a non-standard approach outweighs the gains in code
readability is something you can decide based on the scope of your project.
|
Subsets and Splits
No saved queries yet
Save your SQL queries to embed, download, and access them later. Queries will appear here once saved.