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Python IndentationError - How to refactor?
Question: I am doing a [Project Euler](https://projecteuler.net) question for
programming practice in order to self-teach myself. I know perfectly well
_how_ to do the question mathematically, _as well as_ how to do it
programmatically.
However, I have to have come up with some insane code to do it; 100 nested
loops and Python hilariously raises this error, and probably rightfully so, on
100 levels of indentation:
IndentationError: too many levels of indentation
tally = 0
ceiling = 100
for integer_1 in range(0, 100, 1):
for integer_2 in range(0, 100 - integer_1, 2):
for integer_3 in range(0, 100 - integer_1 - integer_2, 3):
for integer_4 ....
for integer_5 ....
etc.
etc.
all the way to integer_100
I have looked through google for solutions but this issue is so rare it has
almost no literature on the subject and I could only find this other stack
overflow question ( [Python IndentationError: too many levels of
indentation](http://stackoverflow.com/questions/8439572/python-
indentationerror-too-many-levels-of-indentation) ) which I could not find much
useful in for my question.
My question is - is there a way to take my solution and find some workaround
or refactor it in a way that has it work? I am truly stumped.
**EDIT:**
Thanks to nneonneo's answer, I was able to solve the question. My code is here
just for future reference of people looking for ways to properly refactor
their code.
from time import time
t = time()
count_rec_dict = {}
# for finding ways to sum to 100
def count_rec(cursum, level):
global count_rec_dict
# 99 is the last integer that we could be using,
# so prevent the algorithm from going further.
if level == 99:
if cursum == 100:
return 1
else:
return 0
res = 0
for i in xrange(0, 101-cursum, level+1):
# fetch branch value from the dictionary
if (cursum+i, level+1) in count_rec_dict:
res += count_rec_dict[(cursum+i, level+1)]
# add branch value to the dictionary
else:
count_rec_dict[(cursum+i, level+1)] = count_rec(cursum+i, level+1)
res += count_rec_dict[(cursum+i, level+1)]
return res}
print count_rec(0, 0)
print time() - t
which runs in an astonishing 0.041 seconds on my computer. WOW!!!!! I learned
some new things today!
Answer: A recursive solution should do nicely, though I'm certain there is an entirely
different solution to the problem that doesn't require this kind of
manipulation.
def count_rec(cursum, level):
if level == 100:
return 1
res = 0
for i in xrange(0, 100-cursum, level+1):
res += count_rec(cursum+i, level+1)
return res
print count_rec(0, 0)
Interestingly enough, if you _memoize_ this function, it will actually have a
reasonable running time (such is the power of _dynamic programming_). Have
fun!
|
Open and preprocessing file in Python NLTK
Question: Im new to Python NLTK and really need your advise. I want to open my own txt
file and do some preprocessing like replacing words with its regex. I've tried
to do it as in NLTK 2.0 Cookbook
import re
replacement_patterns = [
(r'won\'t', 'will not'),
(r'can\'t', 'cannot'),
(r'i\'m', 'i am'),
(r'ain\'t', 'is not'),
(r'(\w+)\'ll', '\g<1> will'),
(r'(\w+)n\'t', '\g<1> not'),
(r'(\w+)\'ve', '\g<1> have'),
(r'(\w+t)\'s', '\g<1> is'),
(r'(\w+)\'re', '\g<1> are'),
(r'(\w+)\'d', '\g<1> would'),
]
class RegexpReplacer(object):
def __init__(self, patterns=replacement_patterns):
self.patterns = [(re.compile(regex), repl) for (regex, repl) in patterns]
def replace(self, line):
s = line
for (pattern, repl) in self.patterns:
(s, count) = re.subn(pattern, repl, s)
return s
it works perfect but how can I use it with my txt file? I've tried to do my
own way but I think its wrong
import nltk
f=open("C:/nltk_data/file.txt", "rU")
raw=f.readlines()
from replacers import RegexpReplacer
replacer=RegexpReplacer()
replacer.replace(raw)
thx in advance!!!
Answer: I think you want to use the [read
method](http://docs.python.org/tutorial/inputoutput.html) to read all the file
contents into a string first.
|
Eclipse Error: no jogl in java.library.path
Question: So I'm quite new to eclipse (first week of actually trying to use it to
develop stuff.) and I tried to import an example project from
<http://unfoldingmaps.org/> and upon trying to compile their test project I'm
greeted with the error:
Eclipse Error: Exception in thread "Animation Thread"
java.lang.UnsatisfiedLinkError: no jogl in java.library.path
Right now my $path sys var looks like this:
C:\csvn\Python25\;%SystemRoot%\system32;%SystemRoot%;%SystemRoot%\System32\Wbem;%SYSTEMROOT%\System32\WindowsPowerShell\v1.0\;C:\Program Files\SourceGear\Common\DiffMerge\;C:\Program Files\TortoiseSVN\bin;C:\Program Files\MySQL\MySQL Server 6.0\bin; %JAVA_HOME%;%ANT_HOME%\bin
Is there something that I'm missing? Jogl.jar is in the project but it seems
like the project is just skipping over stuff.. help?
Answer: It seems that your application requires some sort of native library, you need
to specify the parameter -Djava.library.path=/path/to/libs on the VM args
field on eclipse.
|
wxPython minimal size of Frame with a Panel
Question: wxpython 2.8.11.0, python 2.7
If i put some `Sizer` with some controls directly into a `Frame` like
import wx
app=wx.App()
frm = wx.Frame(None, title='title')
sizer = wx.BoxSizer(wx.HORIZONTAL)
sizer.Add(wx.SpinCtrl(frm))
sizer.Add(wx.SpinCtrl(frm))
frm.SetSizerAndFit(sizer)
frm.Show()
app.MainLoop()
the `Frame` will automagically have a correct minimum size to contain the
`Sizer` and it is not possible to make it smaller. If there is a `Panel` in
between (as needed for tabbing between controls) this does not work, the
window can be made too small.
import wx
app=wx.App()
frm = wx.Frame(None, title='title')
pan = wx.Panel(frm)
sizer = wx.BoxSizer(wx.HORIZONTAL)
sizer.Add(wx.SpinCtrl(pan))
sizer.Add(wx.SpinCtrl(pan))
pan.SetSizerAndFit(sizer)
frm.Show()
app.MainLoop()
Additionally `frm.Fit()` and `frm.SetMinSize(frm.GetEffectiveMinSize())` are
required to get the same behavior. Full Code:
import wx
app=wx.App()
frm = wx.Frame(None, title='title')
pan = wx.Panel(frm)
sizer = wx.BoxSizer(wx.HORIZONTAL)
sizer.Add(wx.SpinCtrl(pan))
sizer.Add(wx.SpinCtrl(pan))
pan.SetSizerAndFit(sizer)
frm.Fit()
frm.SetMinSize(frm.GetEffectiveMinSize())
frm.Show()
app.MainLoop()
I am okay with `frm.Fit()`, but i dislike
`frm.SetMinSize(frm.GetEffectiveMinSize())`. Isn't there a better solution so
that the `Frame` automatically considers the minimum size of the `Panel` just
like with the `Sizer` before? I'm considered with what happens if the
`EffectiveMinSize` changes after another control is added to the sizer.
**Edit:** Apparently
panel.SetSizerAndFit(sizer)
frm.Fit()
frm.SetMinSize(frm.GetEffectiveMinSize())
should be replaced by
panel.SetSizer(sizer)
sizer.SetSizeHints(frm)
which looks somewhat cleaner. So in total this looks like
import wx
app=wx.App()
frm = wx.Frame(None, title='title')
pan = wx.Panel(frm)
sizer = wx.BoxSizer(wx.HORIZONTAL)
sizer.Add(wx.SpinCtrl(pan))
sizer.Add(wx.SpinCtrl(pan))
pan.SetSizer(sizer)
sizer.SetSizeHints(frm)
frm.Show()
app.MainLoop()
Is this the preferred way to do this?
If widgets are added later on even the first approach with the `Sizer`
directly on the `Frame` doesn't get it right without intervention, so i think
that is a totally different question.
Answer: The most elegant way (IMHO) is given in phineas' answer. It is slightly
inefficient to have an extra otherwise unneeded sizer but I don't think it can
really be noticeable.
Some people do call `SetSizeHints()` manually, as in your last example, and
this works as well and might be more clear (whenever I use an extra sizer I
feel the need to leave a comment explaining why it shouldn't be removed).
Unfortunately there is no better way and I am not sure if we can even add one
because you need to do something with all of the panel, the sizer and the
frame and this means that you can't do it with a single method call without
passing unrelated parameters to it. I.e. we could have something like
panel.SetSizerAndFitParent(sizer, frame);
but it's not really clear whether this would be better.
|
seek to regex in a large file using python
Question: I am trying to seek to a token ':path,' in a file, then read all the following
(arbitrary digit count) numbers as a number (so for ':path,123' I seek to the
, in file then read the integer 123). Then read the chars between the current
seek position and pos+123 (store them in a list or whatever). Then seek until
the next match for ':path,' and repeat the process.
I would like a function a bit like:
def fregseek(FILE, current_seek, /regex/):
.
.
value_found = ? # result of reading next N chars after :path,[0-9]+
.
.
return next_start_seek, value_found
There may be any number of matches for ':path,' in a line, and that string may
occur within the number of chars specified after ','. I have written a messy
bunch of rubbish which reads in each line, then for each line chomps of the
first N chars indicated by the match, then continues processing the string
until it is all eaten up. Then reads the next string and so on.
This is horrible, I do not want to have to slurp off all the lines from a
potentially huge file when all I really need to do is seek (especially since a
newline is irrelevant, so having an extra processing step just because lines
are easy to pull from files is ridiculous).
So, there it is, that is my problem that I would like to solve. I need to seek
to a match, read a value, continue from the end of that value looking for the
next match and so on until the file is exhausted.
If anybody can help me with this I will be happy to hear from them :)
I would like to avoid non-standard libraries if possible, I would also like
the shortest code but this is the least of my concerns (speed and memory
consumption are the important factors, but I don't want 50 loc extra just to
bootstrap some library with a small funciton in it I could just rip out if
only I knew what it was).
I would prefer python code, however, if perl beats python in this regard I
will use perl instead, I am also open to clever sed/awk/bash scripts etc as
long as they are not horribly slower.
Thanks very much in advance.
Answer: You can do it in nearly one line in python:
with open('filename.txt') as f:
text = f.read()
results = [text[i[0]:i[0] + i[1]] for i in
((m.end(), int(m.group(1))) for m in
re.finditer(':path,([0-9]+)', text))]
Note: untested...
|
Python Fabric load config from separate file
Question: I am use python fabric with all configuration in one .fab file.
How can I put sensitive data as password to separate file and then import/load
to fab main file?
Answer: Define a simple function within your fabfile.py to read your passwords out of
a separate file. Something along the lines of:
def new_getpass(username):
with open("/etc/passwd", "r") as f:
for entry in [l.split(":") for l in f.readlines()]:
if entry[0] == username:
return entry
return None
This will return `None` in the event that the username cannot be found and the
entire user's record as a list in the event the user is found.
Obviously my example is getting its data from `/etc/passwd` but you can easily
adapt this basic functionality to your own file:
`credentials.dat`
database1|abcd1234
database2|zyxw0987
And then the above code modified to use this file like this, with the slight
variation to return only the password (since we know the database name):
def getpass(database):
with open("credentials.dat", "r") as f:
for entry in [l.split("|") for l in f.readlines()]:
if entry[0] == username:
return entry[1]
return None
While not as simple as an import, it provides you flexibility to be able to
use plaintext files to store your credentials in.
|
django/python variables inside strings?
Question: I'm new to python and would like some assistance.
I have a variable
q = request.GET['q']
How do I insert the variable `q` inside this:
url = "http://search.com/search?term="+q+"&location=sf"
Now I'm not sure what the convention is? I'm used to PHP or javascript, but
I'm learning python and how do you insert a variable dynamically?
Answer: Use the format method of String:
url = "http://search.com/search?term={0}&location=sf".format(q)
But of course you should URL-encode the q:
import urllib
...
qencoded = urllib.quote_plus(q)
url =
"http://search.com/search?term={0}&location=sf".format(qencoded)
|
pyspotify Segmentation Fault (libspotify)
Question: I am trying to work with pyspotify with but no luck.
Setup:
* Ubuntu - 12.04 TLS - fresh(ish) install
* virtualenv - 1.8.2
* libspotify - 12.1.51
* pyspotiy - dev (1.8)
I have the pyspotify example `jukebox.py` but when I run it it always gives
Segmentation Fault
_(I had this example was working on a separate VM before however need to
replicate the functionality on a fresh VM.)_
$ python jukebox.py -uEMAIL_ADDRESS -pPASSWORD
Logging in, please wait...
Segmentation fault (core dumped)
The `spotify_appkey.key` is in the same folder (it doesn't get as far as the
SegFault without the key).
Additionally I created a script to simply connect to Spotify but this also
gives a Segmentation Fault.
from spotify.manager import
from spotify import SpotifySessionManager
session = SpotifySessionManager(username=EMAIL_ADDRESS, password=PASSWORD)
print('Connecting')
session.connect()
print('Connected')
This also give:
$ python test.py
Session created
Connecting
Segmentation fault (core dumped)
Answer: Try to run `jukebox.py` as root.
|
Virtualenv shell errors
Question: I've just installed virtualenv (with Python 2.7.2) on my Mac, and I followed
the guide here:
<http://virtualenvwrapper.readthedocs.org/en/latest/install.html>
But I now get the following errors when I start up my shell every time:
stevedore.extension Could not load 'user_scripts': distribute
stevedore.extension distribute
Traceback (most recent call last):
File "/Library/Python/2.7/site-packages/stevedore/extension.py", line 62, in __init__
invoke_kwds,
File "/Library/Python/2.7/site-packages/stevedore/extension.py", line 74, in _load_one_plugin
plugin = ep.load()
File "/Library/Python/2.7/site-packages/setuptools-0.6c11-py2.7.egg/pkg_resources.py", line 1953, in load
if require: self.require(env, installer)
File "/Library/Python/2.7/site-packages/setuptools-0.6c11-py2.7.egg/pkg_resources.py", line 1966, in require
working_set.resolve(self.dist.requires(self.extras),env,installer))
File "/Library/Python/2.7/site-packages/setuptools-0.6c11-py2.7.egg/pkg_resources.py", line 565, in resolve
raise DistributionNotFound(req) # XXX put more info here
DistributionNotFound: distribute
stevedore.extension Could not load 'project': distribute
stevedore.extension distribute
Traceback (most recent call last):
File "/Library/Python/2.7/site-packages/stevedore/extension.py", line 62, in __init__
invoke_kwds,
File "/Library/Python/2.7/site-packages/stevedore/extension.py", line 74, in _load_one_plugin
plugin = ep.load()
File "/Library/Python/2.7/site-packages/setuptools-0.6c11-py2.7.egg/pkg_resources.py", line 1953, in load
if require: self.require(env, installer)
File "/Library/Python/2.7/site-packages/setuptools-0.6c11-py2.7.egg/pkg_resources.py", line 1966, in require
working_set.resolve(self.dist.requires(self.extras),env,installer))
File "/Library/Python/2.7/site-packages/setuptools-0.6c11-py2.7.egg/pkg_resources.py", line 565, in resolve
raise DistributionNotFound(req) # XXX put more info here
DistributionNotFound: distribute
stevedore.extension Could not load 'user_scripts': distribute
stevedore.extension distribute
Traceback (most recent call last):
File "/Library/Python/2.7/site-packages/stevedore/extension.py", line 62, in __init__
invoke_kwds,
File "/Library/Python/2.7/site-packages/stevedore/extension.py", line 74, in _load_one_plugin
plugin = ep.load()
File "/Library/Python/2.7/site-packages/setuptools-0.6c11-py2.7.egg/pkg_resources.py", line 1953, in load
if require: self.require(env, installer)
File "/Library/Python/2.7/site-packages/setuptools-0.6c11-py2.7.egg/pkg_resources.py", line 1966, in require
working_set.resolve(self.dist.requires(self.extras),env,installer))
File "/Library/Python/2.7/site-packages/setuptools-0.6c11-py2.7.egg/pkg_resources.py", line 565, in resolve
raise DistributionNotFound(req) # XXX put more info here
DistributionNotFound: distribute
I don't know if it is affecting this problem, but I am using ZSH.
I tried to install stevedore through pip (sudo pip install stevedore), but I
get the following error:
sudo sh setuptools-0.6c11-py2.7.egg
Processing setuptools-0.6c11-py2.7.egg
removing '/Library/Python/2.7/site-packages/setuptools-0.6c11-py2.7.egg' (and everything under it)
Copying setuptools-0.6c11-py2.7.egg to /Library/Python/2.7/site-packages
setuptools 0.6c11 is already the active version in easy-install.pth
Installing easy_install script to /usr/local/bin
Installing easy_install-2.7 script to /usr/local/bin
Installed /Library/Python/2.7/site-packages/setuptools-0.6c11-py2.7.egg
Processing dependencies for setuptools==0.6c11
Finished processing dependencies for setuptools==0.6c11
TXSLs-MacBook-Pro% sudo pip install stevedore --upgrade
Requirement already up-to-date: stevedore in /Library/Python/2.7/site-packages
Downloading/unpacking distribute (from stevedore)
Running setup.py egg_info for package distribute
Installing collected packages: distribute
Running setup.py install for distribute
Before install bootstrap.
Scanning installed packages
Setuptools installation detected at /Library/Python/2.7/site-packages/setuptools-0.6c11-py2.7.egg
Egg installation
Patching...
Renaming /Library/Python/2.7/site-packages/setuptools-0.6c11-py2.7.egg into /Library/Python/2.7/site-packages/setuptools-0.6c11-py2.7.egg.OLD.1348764450.4
Patched done.
Relaunching...
Traceback (most recent call last):
File "<string>", line 1, in <module>
NameError: name 'install' is not defined
Complete output from command /usr/bin/python -c "import setuptools;__file__='/tmp/pip-build/distribute/setup.py';exec(compile(open(__file__).read().replace('\r\n', '\n'), __file__, 'exec'))" install --record /tmp/pip-FAPgYH-record/install-record.txt --single-version-externally-managed:
Before install bootstrap.
Scanning installed packages
Setuptools installation detected at /Library/Python/2.7/site-packages/setuptools-0.6c11-py2.7.egg
Egg installation
Patching...
Renaming /Library/Python/2.7/site-packages/setuptools-0.6c11-py2.7.egg into /Library/Python/2.7/site-packages/setuptools-0.6c11-py2.7.egg.OLD.1348764450.4
Patched done.
Relaunching...
Traceback (most recent call last):
File "<string>", line 1, in <module>
NameError: name 'install' is not defined
----------------------------------------
Command /usr/bin/python -c "import setuptools;__file__='/tmp/pip-build/distribute/setup.py';exec(compile(open(__file__).read().replace('\r\n', '\n'), __file__, 'exec'))" install --record /tmp/pip-FAPgYH-record/install-record.txt --single-version-externally-managed failed with error code 1 in /tmp/pip-build/distribute
Storing complete log in /Users/txsl/Library/Logs/pip.log
I manually installed setuptools as I couldn't install anything through pip
without it.
What has gone wrong here and how can i fix it? The internet doesn't seem to
have many cases of the error with stevedore. I feel rather stuck at the
moment!
Many thanks!
Answer: I also use zsh and had a similar problem. I solved with this:
sudo pip install virtualenv virtualenvwrapper
I have the package `python-pip` installed in my Ubuntu 12.04.
|
I want to fetch json data from a given url And that json data i have to convert into xml form
Question: I want to fetch JSON data from a given url
http://www.deanclatworthy.com/imdb/?=The+Green+Mile
and convert the JSON data into XML. I have used
[`urllib`](http://docs.python.org/library/urllib.html) and
[`json`](http://docs.python.org/library/json.html) to convert JSON objects
into python dictionary.
Here is my code:
import json
json_string = '{"imdbid":"tt0120689","imdburl":"http:\/\/www.imdb.com\/title\/tt0120689\/","genres":"Crime,Drama,Fantasy,Mystery","languages":"English ,French","country":"USA","votes":"281023","stv":0,"series":0,"rating":"8.4","title":"The Green Mile","year":"1999","usascreens":2875,"ukscreens":340}'
new_python_object = json.loads(json_string)
print(json_string)
print()
print (new_python_object)
And the result:
{"imdbid":"tt0120689","imdburl":"http:\/\/www.imdb.com\/title\/tt0120689\/","genres":"Crime,Drama,Fantasy,Mystery","languages":"English ,French","country":"USA","votes":"281023","stv":0,"series":0,"rating":"8.4","title":"The Green Mile","year":"1999","usascreens":2875,"ukscreens":340}
{'ukscreens': 340, 'rating': '8.4', 'genres': 'Crime,Drama,Fantasy,Mystery', 'title': 'The Green Mile', 'series': 0, 'imdbid': 'tt0120689', 'year': '1999', 'votes': '281023', 'languages': 'English ,French', 'stv': 0, 'country': 'USA', 'usascreens': 2875, 'imdburl': 'http://www.imdb.com/title/tt0120689/'}
Answer: Using the [requests](http://docs.python-requests.org/en/latest/) and
[dict2xml](https://github.com/quandyfactory/dict2xml) libraries:
>>> import requests
>>> r = requests.get("http://www.deanclatworthy.com/imdb/?q=The+Green+Mile")
>>> import dict2xml
>>> xml = dict2xml.dict2xml(r.json)
>>> print xml
<country>USA</country>
<genres>Crime,Drama,Fantasy,Mystery</genres>
<imdbid>tt0120689</imdbid>
<imdburl>http://www.imdb.com/title/tt0120689/</imdburl>
<languages>English,French</languages>
<rating>8.5</rating>
<runtime>189min</runtime>
<series>0</series>
<stv>0</stv>
<title>The Green Mile</title>
<ukscreens>340</ukscreens>
<usascreens>2875</usascreens>
<votes>344054</votes>
<year>1999</year>
|
Trying to append items to a list in python but its acting odd
Question: I have events, people can belong an event. So I have an event class that looks
like:
class Event():
name = ""
people = []
I also have a global variable to hold all the events
events = []
Now I'm trying to process my raw data into events and people going to them:
# If there are missions, add the events
for m in wiki.missions:
foundEvent = False
for e in events:
if e.name == m:
foundEvent = True
foundPerson = False
for p in e.people:
if p.rawName == person.rawName:
foundPerson = True
if not foundPerson:
e.people.append(person)
print "Added " + person.display + " to " + m + " (" + str(len(e.people)) + ")"
if foundEvent == False:
event = Event()
event.name = m
event.people.append(person)
print "New " + person.display + " to " + m + " (" + str(len(event.people)) + ")"
events.append(event)
event = None
Based on my print statements I can see who is added to existing event and when
and who makes a new event. The odd thing is the count of people in an event is
always increments the people in all events.
New Joseph M. Acaba to STS-119 (1)
New Joseph M. Acaba to Soyuz TMA-04M (2)
New Joseph M. Acaba to Expedition 31 Expedition 32 (3)
Added Dominic A. Antonelli to STS-119 (4)
New Dominic A. Antonelli to STS-132 (5)
Added Richard R. Arnold to STS-119 (6)
This makes no sense to me, what is it than I am doing wrong? (I'm sure there
is a lot)
Answer: You should be using instance variables instead of class variables. So set up
your class something like this, and modify the rest of your code to fit it:
class Event:
def __init__(self, name):
self.name = name
self.people = []
The important difference here is just as you described: instance variables are
set for a specific instance of the class, whereas class variables are set for
_all_ instances of that class.
|
Python CGI in IIS: issue with urandom function
Question: I’m having a very strange issue with running a python CGI script in IIS.
The script is running in a custom application pool which uses a user account
from the domain for identity. Impersonation is disabled for the site and
Kerberos is used for authentication.
* When the account is member of the `“Domain Admins”` group, everything works like a charm
* When the account is **not** member of `“Domain Admins”`, I get an error on the very first line in the script: `“import cgi”`. It seems like that import eventually leads to a random number being generated and it’s the call to `_urandom()` which fails with a `“WindowsError: [Error 5] Access is denied”`.
* If I run the same script from the command prompt, when logged in with the same user as the one from the application pool, everything works as a charm.
When searching the web I have found out that the `_urandom` on windows is
backed by the `CryptGenRandom` function in the operating system. Somehow it
seems like my python CGI script does not have access to that function when
running from the IIS, while it has access to that function when run from a
command prompt.
To complicate things further, when logging in as the account running the
application pool and then invoking the CGI-script from the web browser it
works. It turns out I have to be logged in with the same user as the
application pool for it to work. As I previously stated, impersonation is
disabled, but somehow it seems like the identity is somehow passed along to
the security functions in windows.
If I modify the `random.py` file that calls the `_urandom()` function to just
return a fixed number, everything works fine, but then I have probably broken
a lot of the security functions in python.
So have anyone experienced anything like this? Any ideas of what is going on?
Answer: I've solved the `_urandom()` error by changing IIS 7.5 settings to
`Impersonate User = yes`. I'm not a Windows admin so I cannot elaborate.
Afterwards `import cgi` inside python script worked just fine.
|
Stepping into a function in IPython
Question: Is there a way to step into the first line of a function in ipython. I imagine
something that would look like:
%step foo(1, 2)
which runs `ipdb` and sets a breakpoint at the first line of `foo`.
If I want to do this now I have to go to the function's source code and add an
`import ipdb; ipdb.set_trace()` line.
Answer: ipdb has had support for runcall, runeval and run since 0.7, earlier this
year. You can use it just like `pdb.runcall`:
In [1]: def foo(a, b):
...: print a + b
...:
In [2]: import ipdb
In [3]: ipdb.runcall(foo, 1, 2)
> <ipython-input-1-2e565fd9c4a4>(2)foo()
1 def foo(a, b):
----> 2 print a + b
3
ipdb>
|
indexing an array
Question: I find myself frequently making indexed lists from flat ones in Python. This
is such a common task that I was wondering if there's a standard utility that
I should be using for it.
The context is this: given an array, I need to create a dict of smaller arrays
using some key for grouping.
e.g:
`["Andy","Alice","Bob","Beth","Charlie"]` becomes
`{"A":["Andy","Alice"],"B":["Bob","Beth"],"C":["Charlie"]}`
My solution looks like this:
def make_index(data,key,value=lambda x:x):
d={}
for item in data:
k = key(item)
v = value(item)
try: d[k].append(v)
except KeyError: d[k]=[v]
return d
It's simple and all, but am I reinventing something that is implemented better
elsewhere?
Answer: You can do the same a little simpler with a
[`defaultdict`](http://docs.python.org/library/collections.html#collections.defaultdict):
from collections import defaultdict
def make_index(data,key,value=lambda x:x):
d=defaultdict(list)
for item in data:
d[key(item)].append(value(item))
return d
Using a `defaultdict` is faster than using `.setdefault()`, which would be the
other option.
|
start python program in the background that can prompt the user for password
Question: Basically I wanted to start a daemon in the background that will still prompt
the user in the console for a password. I created this with pexpect, but when
this program ends it kills the daemon since it is a child process. So
obviously pexpect isn't going to work for this. Does any body know of a way to
do this?
#!/usr/bin/env python
import pexpect
import getpass
child = pexpect.spawn('python daemon.py &')
child.expect_exact('Password:')
passwd = getpass.getpass()
child.sendline(passwd)
index = child.expect_exact('Started Successfully')
print index
Answer: pexpect has a method [close(self,
force=True)](http://pexpect.sourceforge.net/pexpect.html#spawn-close) which
closes its connection to the child process.
According to the documentation, the child pocess is terminated if force=True
so
child.close(force=False)
should disconnect, but leave the application running.
|
Building an HTML Diff/Patch Algorithm
Question: A description of what I'm going to accomplish:
* Input 2 (N is not essential) HTML documents.
* Standardize the HTML format
* Diff the two documents -- external styles are not important but anything inline to the document will be included.
* Determine delta at the HTML Block Element level.
Expanding the last point:
Imagine two pages of the same site that both share a sidebar with what was
probably a common ancestor that has been copy/pasted. Each page has some minor
changes to the sidebar. The diff will reveal these changes, then I can "walk
up" the DOM to find the first common block element shared by them, or just
default to `<body>`. In this case, I'd like to walk it up and find that, oh,
they share a common `<div id="sidebar">`.
I'm familiar with DaisyDiff and the application is similar -- in the CMS
world.
I've also begun playing with the google diff-patch library.
I wanted to give ask this kind of non-specific question to hopefully solicit
any advise or guidance that anybody thinks could be helpful. Currently if you
put a gun to my head and said "CODE IT" I'd rewrite DaisyDiff in Python and
add-in this block-level logic. But I thought maybe there's a better way and
the answers to [Anyone have a diff algorithm for rendered
HTML?](http://stackoverflow.com/questions/31722/anyone-have-a-diff-algorithm-
for-rendered-html) made me feel warm and fuzzy.
Answer: If you were going to start from scratch, a useful search term would be "tree
diff".
There's a pretty awesome blog post [here](http://useless-
factor.blogspot.com/2008/01/matching-diffing-and-merging-xml.html), although I
just found it by googling "daisydiff python" so I bet you've already seen it.
Besides all the interesting theoretical stuff, he mentions the existence of
[Logilab's `xmldiff`](http://www.logilab.org/859), an open-source XML differ
written in Python. That might be a decent starting point — maybe less correct
than trying to wrap or reimplement DaisyDiff, but probably easier to get up
and running quickly.
There's also [html-tree-diff](http://pypi.python.org/pypi/html-tree-
diff/0.1.2) on pypi, which I found via this Quora link:
<http://www.quora.com/Is-there-any-good-Python-implementation-of-a-tree-diff-
algorithm>
There's some theoretical stuff about tree diffing at [efficient diff algorithm
for trees and Levenshtein
distance](http://cstheory.stackexchange.com/questions/10205/efficient-diff-
algorithm-for-trees-and-levenshtein-distance) on cstheory.stackexchange.
BTW, just to clarify, you _are_ talking about diffing two DOM trees, but not
necessarily rendering the diff/merge back into any particular HTML, right?
**(EDIT: Right.)** A lot of the similarly-worded questions on here are really
asking "how can I color deleted lines red and added lines green" or "how can I
make matching paragraphs line up visually", skipping right over the
theoretical hard part of "how do I diff two DOM trees in the first place" and
the practical hard part of "how do I parse possibly malformed HTML into a DOM
tree even before that". :)
|
Is it possible to extract preprocessor information from clang's parse tree?
Question: Consider the following simple header, demo.h:
#define PERSIST
struct Serialised
{
int someTransientValue ;
PERSIST int aNumberToPersist ;
};
I use the following code and Clang's python API to iterate over the header:
import sys, clang.cindex
def callexpr_visitor(node, parent, userdata):
if node.location.file: print node.location.file, node.displayname, node.kind
return 2
tu = clang.cindex.Index.create().parse(sys.argv[1], args=['-x', 'c++'])
clang.cindex.Cursor_visit(tu.cursor, clang.cindex.Cursor_visit_callback(callexpr_visitor), None)
This prints out the elements of Clang's AST, producing the following output:
> demo.h Serialised CursorKind.STRUCT_DECL
> demo.h someTransientValue CursorKind.FIELD_DECL
> demo.h aNumberToPersist CursorKind.FIELD_DECL
Does anyone know how I can extract the preprocessor declaration associated
with the member variable called 'aNumberToPersist'?, is there a better way to
'tag' variables in a manner that manifests clearly in the parse tree?
Xubuntu 12.04, clang version 3.1 (tags/RELEASE_31/final), Target:
x86_64-unknown-linux-gnu Thread model: posix.
Answer: I would probably say: not this way.
Macros are not represented in the AST per se. Types, Attributes, etc... all
those elements that have _semantic_ values are represented (and comments), and
optionally you can query whether some of them were expanded from a macro and
get back that original macro spelling; however macros in themselves do not
appear in the AST, at all.
If you could, it might be more interesting to _extend_ Clang with a new
**attribute** , especially in C++11: `[[gearoid::persist]]`. C++11 requires
that compilers ignore attributes they know not about, so by "namespacing" your
own attributes you pretty much guarantee that only you will care about their
meaning.
I know not, unfortunately, whether you will need to teach Clang about your
attributes so they are represented in the AST ([Michael
Han](http://lists.cs.uiuc.edu/pipermail/cfe-dev/2012-October/024637.html) is
working on always memorizing them). In any case, you may get more useful
answers on the [Clang DEV](http://lists.cs.uiuc.edu/mailman/listinfo/cfe-dev)
mailing list (unfortunately, there is no Clang Users mailing list).
**EDIT** : Just [landed today](http://llvm.org/viewvc/llvm-
project?view=rev&revision=165082)! Clang will now retain all attributes (even
those it does not understand) in its AST.
|
Problems with PYTHONPATH
Question: From the command line (Mac OS), when I execute 'echo $PYTHONPATH' I get:
> /opt/local/Library/Frameworks/Python.framework/Versions/2.7/lib/python2.7
If I then enter the Python interpreter and do the following:
>>> import os
>>> os.environ['PYTHONPATH']
Traceback (most recent call last):
File "<stdin>", line 1, in <module>
File "/opt/local/Library/Frameworks/Python.framework/Versions/2.7/lib/python2.7/UserDict.py", line 23, in __getitem__
raise KeyError(key)
KeyError: 'PYTHONPATH'
Why would this happen?
Answer: You forgot to export it to the environment so that subprocesses can access it;
it's currently only a bash variable.
export PYTHONPATH
|
numpy.shape gives inconsistent responses - why?
Question: I'm a newbie to python. What I would like to know is, Why does the program
import numpy as np
c = np.array([1,2])
print(c.shape)
d = np.array([[1],[2]]).transpose()
print(d.shape)
give
(2,)
(1,2)
as its output? Shouldn't it be
(1,2)
(1,2)
instead? I got this in both python 2.7.3 and python 3.2.3
Thanks!
Answer: When you invoke the `.shape` attribute of a `ndarray`, you get a tuple with as
many elements as dimensions of your array. The length, ie, the number of rows,
is the first dimension (`shape[0]`)
* You start with an array : `c=np.array([1,2])`. That's a plain 1D array, so its shape will be a 1-element tuple, and `shape[0]` is the number of elements, so `c.shape = (2,)`
* Consider `c=np.array([[1,2]])`. That's a 2D array, with 1 row. The first and only row is `[1,2]`, that gives us two columns. Therefore, `c.shape=(1,2)` and `len(c)=1`
* Consider `c=np.array([[1,],[2,]])`. Another 2D array, with 2 rows, 1 column: `c.shape=(2,1)` and `len(c)=2`.
* Consider `d=np.array([[1,],[2,]]).transpose()`: this array is the same as `np.array([[1,2]])`, therefore its shape is `(1,2)`.
Another useful attribute is `.size`: that's the number of elements across all
dimensions, and you have for an array `c` `c.size = np.product(c.shape)`.
More information on the shape in the
[documentation](http://www.scipy.org/Tentative_NumPy_Tutorial#head-62ef2d3c0a5b4b7d6fdc48e4a60fe48b1ffe5006).
|
Add two 3D numpy arrays with a 2D mask
Question: I would like to add two 3D numpy arrays (RGB image arrays) with a 2D mask
generated by some algorithms on a greyscale image. What is the best way to do
this?
As an example of what I am trying to do:
from PIL import Image, ImageChops, ImageOps
import numpy as np
img1=Image.open('./foo.jpg')
img2=Image.open('./bar.jpg')
img1Grey=ImageOps.grayscale(img1)
img2Grey=ImageOps.grayscale(img2)
# Some processing for example:
diff=ImageChops.difference(img1Grey,img2Grey)
mask=np.ma.masked_array(img1,diff>1)
img1Array=np.asarray(im1)
img2Array=np.asarray(im2)
imgResult=img1Array+img2Array[mask]
I was thinking:
1) break up the RGB image and do each color separately
2) duplicate the mask into a 3D array
or is there a more pythonic way to do this?
Thanks in advance!
Answer: Wish I could add a comment instead of an answer. Anyhow:
masked_array is _not_ for making masks. It's for including only the data
outside the mask in calculations such as sum, mean, etc.. scientific
statistical applications. It's comprised of an array and the mask for the
array. It's probably NOT what you want.
You probably just want a normal boolean mask, as in:
mask = diff>1
Then you'll need to modify the shape so numpy broadcasts in the correct
dimension, then broadcast it into the 3rd dimension:
mask.shape = mask.shape + (1,)
mask = np.broadcast_arrays(img1Array, mask)[1]
After that, you can just add the pixels:
img1Array[mask] += img2Array[mask]
A further point of clarification:
imgResult=img1Array+img2Array[mask]
That could never work. You are saying 'add some of the pixels from img2Array
to _all_ of the pixels in img1Array' 6_9
If you want to apply a ufunc between two or more arrays, they must be either
the same shape, or broadcastable to the same shape.
|
Running a timer for few minutes in python
Question: I am trying to run a certain function "foo" every second. I have to do this
for a few minutes (say 5).
The function foo() makes 100 HTTP Requests (which contains a JSON object) to
the server and prints the JSON response.
In short, I have to make 100 HTTP requests per second for 5 minutes.
I have just started learning python, thus don't have extensive knowledge. This
is what I have tried:
import threading
noOfSecondsPassed = 0
def foo():
global noOfSecondsPassed
# piece of code which makes 100 HTTP requests (I use while loop)
noOfSecondsPassed += 1
while True:
if noOfSecondsPassed < (300) # 5 minutes
t = threading.Timer(1.0, foo)
t.start()
Due to multiple threads, the function foo isn't called 300 times but much much
more than that. I have tried setting a lock too:
def foo():
l = threading.Lock()
l.acquire()
global noOfSecondsPassed
# piece of code which makes 100 HTTP requests (I use while loop)
noOfSecondsPassed += 1
l.release()
Rest of code is same as the previous code snippet. But this also does not
work.
How do I do this?
**Edit: Different Approach**
I have tried this approach which worked for me:
def foo():
noOfSecondsPassed = 0
while noOfSecondsPassed < 300:
#Code to make 100 HTTP requests
noOfSecondsPassed +=1
time.sleep(1.0)
foo()
Any disadvantages in doing so?
Answer: I would use another approach which is easier I think.
Create 300 timer thread, each running 1 sec after the previous. The main loop
is executed in almost an instant so the error factor is very low. Here's a
sample Demo:
import datetime
import thread
import threading
def foo():
print datetime.datetime.now()
print threading.active_count()
for x in range(0,300):
t = threading.Timer(x + 1, foo)
t.start()
This code output should look like this:
2012-10-01 13:21:07.328029
301
2012-10-01 13:21:08.328281
300
2012-10-01 13:21:09.328449
299
2012-10-01 13:21:10.328615
298
2012-10-01 13:21:11.328768
297
2012-10-01 13:21:12.329006
296
2012-10-01 13:21:13.329289
295
2012-10-01 13:21:14.329369
294
2012-10-01 13:21:15.329580
293
2012-10-01 13:21:16.329793
292
2012-10-01 13:21:17.329958
291
2012-10-01 13:21:18.330138
290
2012-10-01 13:21:19.330300
289
...
As you can see, each thread is launched about 1 sec after the previous and you
are starting exactly 300 threads.
|
How to Change Content-Type Python
Question: I want to upload a file to a remote device. If i look up the connection with
wireshark i get this
POST /saveRestore.htm.cgi HTTP/1.1
Host: 10.128.115.214
User-Agent: Mozilla/5.0 (X11; Ubuntu; Linux i686; rv:15.0) Gecko/20100101 Firefox/15.0.1
Accept: text/html,application/xhtml+xml,application/xml;q=0.9,*/*;q=0.8
Accept-Language: de-de,de;q=0.8,en-us;q=0.5,en;q=0.3
Accept-Encoding: gzip, deflate
Connection: keep-alive
Referer: http://10.128.115.214/saveRestore.htm
Cache-Control: max-age=0
Content-Type: multipart/form-data; boundary=---------------------------961265085509552220604142744
Content-Length: 10708
-----------------------------961265085509552220604142744
Content-Disposition: form-data; name="restore"; filename="config(2).cfg"
Content-Type: application/octet-stream
Now this says that that the browser only accepts
text/html,application/xhtml+xml,application/xml;q=0.9,_/_ ;q=0.8
If i upload the file with my script it says
--0a7125aebb8845ba8ab9aa21306b01f6
Content-Disposition: form-data; name="restore"; filename="Config.cfg"
Content-Type: text/plain; charset=utf-8
So it's a wrong file type..
so how do i change the content-type of the File ?
My code looks so far as follows:
#!/usr/bin/python
import httplib
import urllib2
from poster.encode import multipart_encode
import poster
from poster.streaminghttp import register_openers
register_openers()
params = {'restore': open("Config.cfg", "rb"), 'upload': 'PC ==>; Unit'}
datagen, headers = multipart_encode(params)
request = urllib2.Request('http://10.128.115.214/saveRestore.htm.cgi', datagen, headers)
u = urllib2.urlopen(request)
print u.read()
Answer: In the [documentation for
`poster.encode.MultipartParam`](http://atlee.ca/software/poster/poster.encode.html#poster.encode.MultipartParam)
it says:
> If `filetype` is set, it is used as the Content-Type for this parameter. If
> unset it defaults to “text/plain; charset=utf8”
So instead of specifying your parameters like this:
params = {'restore': open("Config.cfg", "rb"), 'upload': 'PC ==>; Unit'}
specify them like this:
params = [MultipartParam('restore', open("Config.cfg", "rb"),
filetype = 'application/octet-stream'),
('upload', 'PC ==>; Unit')]
|
Popen stdout reading pipe, deadlock using sleep
Question: Well, I have two scripts. The a.py which prints the output of the b.py script
as follows:
#a.py
from subprocess import Popen, PIPE, STDOUT
p = Popen(['/Users/damian/Desktop/b.py'], shell=False, stdout=PIPE, stderr=STDOUT)
while p.poll() is None:
print p.stdout.readline()
#b.py
#!/usr/bin/env python
import time
while 1:
print 'some output'
#time.sleep(1)
This works.But, Why do my scripts deadlock when I uncomment the time.sleep()
line?
Answer: Your output is probably buffered. Add a
[.flush()](http://docs.python.org/library/stdtypes.html#file.flush) for stdout
to clear it:
import sys
import time
while 1:
print 'someoutput'
sys.stdout.flush()
time.sleep(1)
|
python enums with attributes
Question: Consider:
class Item:
def __init__(self, a, b):
self.a = a
self.b = b
class Items:
GREEN = Item('a', 'b')
BLUE = Item('c', 'd')
Is there a way to adapt the ideas for simple enums to this case? (see [this
question](http://stackoverflow.com/questions/36932/whats-the-best-way-to-
implement-an-enum-in-python)) Ideally, as in Java, I would like to cram it all
into one class.
Java model:
enum EnumWithAttrs {
GREEN("a", "b"),
BLUE("c", "d");
EnumWithAttrs(String a, String b) {
this.a = a;
this.b = b;
}
private String a;
private String b;
/* accessors and other java noise */
}
Answer: Use a
[namedtuple](http://docs.python.org/library/collections.html#collections.namedtuple):
from collections import namedtuple
Item = namedtuple('abitem', ['a', 'b'])
class Items:
GREEN = Item('a', 'b')
BLUE = Item('c', 'd')
|
Writing a python Dictionary to a CSV file with keys as column headers
Question: I'm trying to write the elements in my dictionary into a text file where each
key would be a column. Currently have I something that looks like
import csv
import numpy as np
data1 = np.arange(10)
data2 = np.arange(10)*2
data3 = np.arange(10)*3
writefile = '../Desktop/data.txt'
datadict = {}
datadict['data1'] = data1
datadict['data2'] = data2
datadict['data3'] = data3
f = open( writefile, 'w' )
fieldnames = ['data1','data2', 'data3']
data = csv.DictWriter(writefile, fieldnames, restval='', extrasaction='ignore', dialect='excel')
f.close()
but it gives me the error "argument 1 must have a "write" method". I'm not
sure what that means. I'm also worried about the dialect = 'excel', but I'm
not sure what else to put. In the end I'd like a file that has something
looking like:
Thanks
Answer: No need to use DictWriter here at all:
import csv
import numpy as np
data1 = np.arange(10)
data2 = np.arange(10)*2
data3 = np.arange(10)*3
writefile = '../test.csv'
fieldnames = ['data1','data2', 'data3']
with open( writefile, 'w' ) as f:
writer = csv.writer(f)
writer.writerow(fieldnames)
writer.writerows(zip(data1, data2, data3))
|
Clean up code when Ctrl+C is caught in python
Question: By registering the signal handler, I can put my clean up code in
signal_handler
signal.signal(signal.SIGINT, signal_handler)
But the problem is when user presses ctrl+c multiple times, the signal handler
run multiple times and the clean up goes crazy.
**My problem is that, how can I make sure that the clean up handler is being
ran once only before exit.**
Here is my trial using lock, but deadlock is occured
def cleanup_handler():
lock.acquire()
if not done:
try:
cleanup()
done = True
finally:
print "release lock"
lock.release()
The problem is that finally block is never ran (that is I can't see the
"release lock" being printed).
**Remark**
After doing a little experiment, it seems that the signaler handler is not
being ran at the same time. When new Ctrl+C is received, the old handler is
killed and a new handler is ran. Am I correct? If yes, the problem becomes
more complicated as I don't want my handler ends in the middle of the....
Answer: You could use a decorator that prevents your function from being run more than
once:
from functools import wraps
def run_once(function):
@wraps(function)
def wrapper(*args):
if not wrapper.has_run:
wrapper.has_run = True
return function()
wrapper.has_run = False
return wrapper
Like so:
@run_once
def signal_handler():
print 'Exit'
|
Selectively dump object attributes with PyYAML
Question: I can use YAML to dump a hierarchy of python objects, so:
import yaml
class C():
def __init__(self, x, y):
self.x = x
self.y = y
class D():
def __init__(self, c, d):
self.c = c
self.d = d
d = D(c=C(x=1, y='hi'),
d='bye')
print yaml.dump(d)
produces the output:
!!python/object:__main__.D
c: !!python/object:__main__.C {x: 1, y: hi}
d: bye
But I want to selectively hide some attributes. So suppose I have a function
`attribs_to_dump(obj)` which for any object returns the list of attribute
names I want to dump, for example:
def attribs_to_dump(obj):
if obj.__class__ == C: return ['x']
if obj.__class__ == D: return ['c']
My question is, how do I hook `attribs_to_dump` into `yaml.dump` so that I get
the following output?
!!python/object:__main__.D
c: !!python/object:__main__.C {x: 1}
There's a complicating factor: I want to achieve the effect by hooking into
Yaml as it crawls over the object hierarchy rather than by pre-processing the
object hierarchy myself. The reason is that not all objects in the hierarchy
are easily amenable to introspection due to `setattr/getattr/__dict__` magic
that is present in some libraries I am using :-(...
All help much appreciated!
Answer: This is an interesting question, I enjoyed solving it, thanks :)
from copy import deepcopy
class C(object):
def __init__(self, x, y):
self.x = x
self.y = y
class D(object):
def __init__(self, c, d):
self.c = c
self.d = d
d = D(
c=C(x=1, y='hi'),
d='bye'
)
FILTER_PARAMS = (
#(class_reference, process_recursively, ['attributes', 'on', 'whitelist'])
(D, True, ['c']),
(C, False, ['x']),
)
def attr_filter(obj, filter_params):
for attr in dir(obj):
if attr.startswith('__'):
# ignore builtins
continue
attr_val = obj.__getattribute__(attr)
# loop through filter params
for (cls, do_recursive, whitelist) in filter_params:
if isinstance(obj, cls) and attr in whitelist:
# filter class matches the current obj's class and
# current attribute is on the whitelist
if do_recursive:
# must process this attribute the same way as the parent
setattr(obj, attr, attr_filter(attr_val, filter_params))
# break will avoid the execution of the else clause meaning
# the attribute was on the white list so don't delete it
break
else:
# delete the current attribute of the instance as it was
# not on the whitelist
delattr(obj, attr)
return obj
# do a deepcopy of the object you pass in, so the original will be preserved
filtered_instance = attr_filter(deepcopy(d), FILTER_PARAMS)
print dir(filtered_instance)
print dir(filtered_instance.c)
# now pass filtered_instance to yaml's dump function
|
How to get the content from a certain <table> using python?
Question: I have some `<tr>`s, like this:
<tr align=center><td>10876151</td><td><a href=userstatus?user_id=yangfanhit>yangfanhit</a></td><td><a href=problem?id=3155>3155</a></td><td><font color=blue>Accepted</font></td><td>344K</td><td>219MS</td><td>C++</td><td>3940B</td><td>2012-10-02 16:42:45</td></tr>
<tr align=center><td>10876150</td><td><a href=userstatus?user_id=BandBandRock>BandBandRock</a></td><td><a href=problem?id=2503>2503</a></td><td><font color=blue>Accepted</font></td><td>16348K</td><td>2750MS</td><td>G++</td><td>840B</td><td>2012-10-02 16:42:25</td></tr>
I want to fetch the content without html tags, like:
yangfanhit
3155
Accepted
344K
219MS
C++
3940B
2012-10-02 16:42:45
Now I'm using the following code to deal with it:
response = urllib2.urlopen('http://poj.org/status', timeout=10)
html = response.read()
response.close()
pattern = re.compile(r'<tr align.*</tr>')
match = pattern.findall(html)
pat = re.compile(r'<td>.*?</td>')
p = re.compile(r'<[/]?.*?>')
for item in match:
for i in pat.findall(item):
print p.sub(r'', i)
print '================================================='
I'm new to regex and also new to python. So could you suggest some better
methods to process it?
Answer: You could use
[`BeautifulSoup`](http://www.crummy.com/software/BeautifulSoup/bs4/doc/) to
parse the html. To write the content of the table in csv format:
#!/usr/bin/env python
import csv
import sys
import urllib2
from bs4 import BeautifulSoup # $ pip install beautifulsoup4
soup = BeautifulSoup(urllib2.urlopen('http://poj.org/status'))
writer = csv.writer(sys.stdout)
for tr in soup.find('table', 'a')('tr'):
writer.writerow([td.get_text() for td in tr('td')])
### Output
Run ID,User,Problem,Result,Memory,Time,Language,Code Length,Submit Time
10876151,yangfanhit,3155,Accepted,344K,219MS,C++,3940B,2012-10-02 16:42:45
10876150,BandBandRock,2503,Accepted,16348K,2750MS,G++,840B,2012-10-02 16:42:25
|
Communicating with a hardware offering a Python interface using iOS
Question: I have to access a hardware component that exposes the following Python
interface:
$ python
>>> from ***.***.***.*** import *
>>> client = Client('http://*****')
>>> client.getFirmwareVersion()
How I can do it?
Do I have to create new class in obj-c or I can use the python library and
access the data using objective-c?
Answer: You seem to be missing an important point; the hardware you are connecting
actually stays entirely remote from the iOS perspective - even if it was
connected via TCP/IP via a local wifi hotspot.
Have a look at
[NSURLConnection](https://developer.apple.com/library/ios/#documentation/Cocoa/Reference/Foundation/Classes/NSURLConnection_Class/Reference/Reference.html),
that is an iOS system component that allows you to remotely connect and
transmit data via TCP/IP in both directions.
Your first task will be finding a proper interface for your Python driven
hardware. I would strongly suggest you to use some kind of an HTTP-interface.
|
How can I download only metadata from a Google Sites API content feed?
Question: I want to download a list of URLs for pages in my Google Sites site. I'm using
the Python API to do this. It seems to be slower than I would expect, and so I
think it's actually downloading the whole content for each entry rather than
just the metadata. Is there any way to download just the metadata? My code is
below:
import gdata.sites.client
client = gdata.sites.client.SitesClient(site='mysite', domain='mydomain.com')
client.ClientLogin('[email protected]', 'password', 'test')
feed = client.GetContentFeed()
for entry in feed.entry:
print entry.GetAlternateLink().href
Answer: The closest approximation is
https://sites.google.com/site/(your site name)/system/feeds/sitemap
Unfortunately, this API doesn't allow the use of `fields` as some newer Google
APIs do.
|
time.sleep hangs multithread function in python
Question: I am having trouble with a sleep statement hanging my multithreading function.
I want my function to go about it's buisness while the rest of the program
runs. Here is a toy that recreates my problem:
import multiprocessing, sys, time
def f(icount, _sleepTime = 1):
for i in range(icount):
time.sleep(_sleepTime)
print(_sleepTime)
def main(args):
m = multiprocessing.Process(target = f, args=(4, ))
m.run()
# f should be sleeping for 1 second so this print statement should come first
print(m.is_alive())
if __name__ == "__main__":
sys.exit(main(sys.argv[1:]))
can anyone explain why this code outputs:
1
1
1
1
False
instead of:
True
1
1
1
1
## #
EDIT
## #
I eventually want to run this function on a schedual, and test if it is
running before I execute the function. This is an example:
import multiprocessing, sys, time
def f(icount, _sleepTime = 1):
for i in range(icount):
time.sleep(_sleepTime)
print(_sleepTime)
def main(args):
m = multiprocessing.Process(target = f, args=(4, ))
for i in range(15):
time.sleep(.5)
if not m.is_alive():
# m.start throws an error after first run
m.run()
print("{}".format(m.is_alive()))
if __name__ == "__main__":
sys.exit(main(sys.argv[1:]))
Answer: Use `start` and `join` instead of `run`:
import multiprocessing, sys, time
def f(icount, _sleepTime = 1):
for i in range(icount):
time.sleep(_sleepTime)
print(_sleepTime)
def main(args):
m = multiprocessing.Process(target = f, args=(4, ))
m.start()
# f should be sleeping for 1 second so this print statement should come first
print(m.is_alive())
m.join()
if __name__ == "__main__":
sys.exit(main(sys.argv[1:]))
#
EDIT
#
Again, use `start` and `join` instead of `run`:
import multiprocessing, sys, time
def f(icount, _sleepTime = 1):
for i in range(icount):
time.sleep(_sleepTime)
print(_sleepTime)
def create_process():
return multiprocessing.Process(target = f, args=(4, ))
def main(args):
m = create_process()
m.start()
for i in range(15):
time.sleep(.5)
if not m.is_alive():
# m.start throws an error after first run
print("restarting")
m.join()
m = create_process()
m.start()
print("{}".format(m.is_alive()))
m.join()
if __name__ == "__main__":
sys.exit(main(sys.argv[1:]))
|
Python PIL reading PNG from STDIN
Question: I am having a problem reading png images from STDIN using PIL. When the image
is written by PIL it is all [scrambled](http://cl.ly/image/3z1k2B1J3F0t), but
if I write the file using simple file open, write and close the file is saved
[perfectly](http://cl.ly/image/3i1w2C0I1o30).
I have a program that dumps png files to stdout in a sequence, with no
compression, and I read that stream using a python script which is suposed to
read the data and do some routines on almost every png. The program that dumps
the data writes a certain string to delimiter the PNGs files, the string is
`"{fim:FILE_NAME.png}"`
The script is something like:
import sys
import re
from PIL import Image
png = None
for linha in sys.stdin:
if re.search('{fim:', linha):
fname = linha.replace('{fim:','')[:-2]
# writes data directly to file, works fine
#f = open("/tmp/%s" % fname , 'w')
#f.write(png)
#f.close()
# create a PIL Image from data and writes to disk, fails fine
im = Image.frombuffer("RGB",(640,480),png, "raw", "RGB", 0, 1)
#im = Image.fromstring("RGB",(640,480),png)
im.save("/tmp/%s" % fname)
png = None
else:
if png is None:
png = linha
else:
png+= linha
imagemagick identify from a wrong image:
> /tmp/1349194042-24.png PNG 640x480 640x480+0+0 8-bit DirectClass 361KiB
> 0.010u 0:00.019
imagemagick identify from a working image:
> /tmp/1349194586-01.png PNG 640x480 640x480+0+0 8-bit DirectClass 903KiB
> 0.010u 0:00.010
Does any one have an idea of what is happening? Is it something about
little/big endians? I have tried `Image.frombuffer`, `Image.fromstring`,
different modes, but nothing. It seems that there is more information on the
buffer that the PIL expects.
Thanks,
Answer: If the `png` variable contains the binary data from a PNG file, you can't read
it using `frombuffer`: that is used for reading raw pixel data. Instead, use
`StringIO` and `Image.open`, i.e.:
img = Image.open(StringIO.StringIO(png))
|
App Engine, PIL and overlaying text
Question: I'm trying to overlay some text over an image on GAE. Now they expose the PIL
library it should not be problem.
Here's what I have. It works, but I can't help think I should be writing
directly to the background image rather than creating a separate overlay image
and then merging.
Can I use
[Image.frombuffer](http://www.pythonware.com/library/pil/handbook/image.htm)
or something, I've given it a go but I'm just not getting it...
from PIL import Image, ImageDraw, ImageFont
from google.appengine.api import images
from google.appengine.ext import blobstore
from google.appengine.api import files
def compose(key):
# create new image
text_img = Image.new('RGBA', (800,600), (0, 0, 0, 0))
draw = ImageDraw.Draw(text_img)
draw.text((0, 0), 'HELLO TEXT', font=ImageFont.load_default())
# no write access on GAE
output = StringIO.StringIO()
text_img.save(output, format="png")
text_layer = output.getvalue()
output.close()
# read background image
blob_reader = blobstore.BlobReader(key)
background = images.Image(blob_reader.read())
# merge
merged = images.composite([(background, 0, 0, 1.0, images.TOP_LEFT),
(text_layer, 0, 0, 1.0, images.TOP_LEFT)],
800, 600)
# save
file_name = files.blobstore.create(mime_type='image/png')
with files.open(file_name, 'a') as f:
f.write(merged)
files.finalize(file_name)
Answer: You should use the `[Image.open][1]` method instead. `Image.frombuffer` and
`Image.fromstring` decode pixel data not raw images.
In your case you could use something like:
blob_reader = blobstore.BlobReader(key)
text_img = Image.open(blob_reader)
.........
|
Cython and fortran - how to compile together without f2py
Question: **FINAL UPDATE**
This question is about how to write a `setup.py` that will compile a cython
module which accesses FORTRAN code directly, like C would. It was a rather
long and arduous journey to the solution, but the full mess is included below
for context.
**ORIGINAL QUESTION**
I have an extension which is a Cython file, which sets up some heap memory and
passes it to the fortran code, and a fortran file, which is a venerable old
module that I'd like to avoid reimplementing if I can.
The `.pyx` file compiles fine to C, but the cython compiler chokes on the
`.f90` file with the following error:
$ python setup.py build_ext --inplace
running build_ext
cythoning delaunay/__init__.pyx to delaunay/__init__.c
building 'delaunay' extension
error: unknown file type '.f90' (from 'delaunay/stripack.f90')
Here's (the top half of) my setup file:
from distutils.core import setup, Extension
from Cython.Distutils import build_ext
ext_modules = [
Extension("delaunay",
sources=["delaunay/__init__.pyx",
"delaunay/stripack.f90"])
]
setup(
cmdclass = {'build_ext': build_ext},
ext_modules = ext_modules,
...
)
_NOTE: I originally had the fortran file's location incorrectly specified
(without the directory prefix) but this breaks in exactly the same way after I
fixed that._
**Things I have tried:**
I found [this](http://stackoverflow.com/questions/6523767/how-do-i-get-setup-
py-test-to-use-a-specific-fortran-compiler), and tried passing in the name of
the fortran compiler (i.e. gfortran) like this:
$ python setup.py config --fcompiler=gfortran build_ext --inplace
usage: setup.py [global_opts] cmd1 [cmd1_opts] [cmd2 [cmd2_opts] ...]
or: setup.py --help [cmd1 cmd2 ...]
or: setup.py --help-commands
or: setup.py cmd --help
error: option --fcompiler not recognized
And I've also tried removing `--inplace`, in case that was the problem (it
wasn't, same as the top error message).
So, how do I compile this fortran? Can I hack it into a `.o` myself and get
away with linking it? Or [is this a bug in
Cython](https://groups.google.com/forum/?fromgroups=#!topic/cython-
users/DP_FksDi6iM), which will force me to reimplement distutils or hack
around with the preprocessor?
**UPDATE**
So, having checked out the `numpy.distutils` packages, I understand the
problem a bit more. It seems that you have to
1. Use cython to convert the .pyx files to cpython .c files,
2. Then use an `Extension`/`setup()` combination that supports fortran, like `numpy`'s.
Having tried this, my `setup.py` now looks like this:
from numpy.distutils.core import setup
from Cython.Build import cythonize
from numpy.distutils.extension import Extension
cy_modules = cythonize('delaunay/sphere.pyx')
e = cy_modules[0]
ext_modules = [
Extension("delaunay.sphere",
sources=e.sources + ['delaunay/stripack.f90'])
]
setup(
ext_modules = ext_modules,
name="delaunay",
...
)
(note that I've also restructured the module a bit, since seemingly an
`__init__.pyx` is disallowed...)
Now is where things become buggy and platform-dependent. I have two testing
systems available - one Mac OS X 10.6 (Snow Leopard), using Macports Python
2.7, and one Mac OS X 10.7 (Lion) using the system python 2.7.
On Snow Leopard, the following applies:
This means that the module compiles (hurray!) (although there's no `--inplace`
for numpy, it seems, so I had to system-wide install the testing module :/)
but I still get a crash on `import` as follows:
>>> import delaunay
Traceback (most recent call last):
File "<input>", line 1, in <module>
File "<snip>site-packages/delaunay/__init__.py", line 1, in <module>
from sphere import delaunay_mesh
ImportError: dlopen(<snip>site-packages/delaunay/sphere.so, 2): no suitable image found. Did find:
<snip>site-packages/delaunay/sphere.so: mach-o, but wrong architecture
and on Lion, I get a compile error, following a rather confusing looking
compile line:
gfortran:f77: build/src.macosx-10.7-intel-2.7/delaunay/sphere-f2pywrappers.f
/usr/local/bin/gfortran -Wall -arch i686 -arch x86_64 -Wall -undefined dynamic_lookup -bundle build/temp.macosx-10.7-intel-2.7/delaunay/sphere.o build/temp.macosx-10.7-intel-2.7/build/src.macosx-10.7-intel-2.7/delaunay/spheremodule.o build/temp.macosx-10.7-intel-2.7/build/src.macosx-10.7-intel-2.7/fortranobject.o build/temp.macosx-10.7-intel-2.7/delaunay/stripack.o build/temp.macosx-10.7-intel-2.7/build/src.macosx-10.7-intel-2.7/delaunay/sphere-f2pywrappers.o -lgfortran -o build/lib.macosx-10.7-intel-2.7/delaunay/sphere.so
ld: duplicate symbol _initsphere in build/temp.macosx-10.7-intel-2.7/build/src.macosx-10.7-intel-2.7/delaunay/spheremodule.o ldand :build /temp.macosx-10.7-intelduplicate- 2.7symbol/ delaunay/sphere.o _initsphere in forbuild architecture /i386
temp.macosx-10.7-intel-2.7/build/src.macosx-10.7-intel-2.7/delaunay/spheremodule.o and build/temp.macosx-10.7-intel-2.7/delaunay/sphere.o for architecture x86_64
Now let's just step back a moment before we pore over the details here.
Firstly, I know there are a bunch of headaches over architecture clashes in
64-bit Mac OS X; I had to work very hard to get Macports Python working on the
Snow Leopard machine (just to upgrade from system python 2.6). I also know
that when you see `gfortran -arch i686 -arch x86_64` you are sending mixed
messages to your compiler. There are all manner of platform-specific problems
buried in there, that we don't need to worry about in the context of this
question.
_But let's just look at this line_ : `gfortran:f77:
build/src.macosx-10.7-intel-2.7/delaunay/sphere-f2pywrappers.f`
**what is numpy doing?!** I don't need any f2py features in this build! I
actually wrote a cython module _in order to avoid_ dealing with f2py's
insanity (I need to have 4 or 5 output variables, as well as neither-in-nor-
out arguments - neither of which is well supported in f2py.) I just want it to
compile `.c` -> `.o`, and `.f90` -> `.o` and link them. I could write this
compiler line myself if I knew how to include all the relevant headers.
Please tell me I don't need to write my own makefile for this... or that
there's a way to translate fortran to (output-compatible) C so I can just
avoid python ever seeing the .f90 extension (which fixes the whole problem.)
Note that [`f2c`](http://www.netlib.org/f2c/) is not suitable for this as it
only works on F77 and this is a more modern dialect (hence the `.f90` file
extension).
**UPDATE 2** The following bash script will happily compile and link the code
in place:
PYTHON_H_LOCATION="/opt/local/Library/Frameworks/Python.framework/Versions/2.7/include/python2.7/"
cython sphere.pyx
gcc -arch x86_64 -c sphere.c -I$PYTHON_H_LOCATION
gfortran -arch x86_64 -c stripack.f90
gfortran -arch x86_64 -bundle -undefined dynamic_lookup -L/opt/local/lib *.o -o sphere.so
Any advice on how to make this kind of hack compatible with a setup.py? I
don't anyone installing this module to have to go find `Python.h` manually...
Answer: **UPDATE:** I've created a project on github which wraps up this generating of
compile lines by hand. it's called [complicated_build](https://github.com/joe-
jordan/complicated_build).
**UPDATE 2:** in fact, "generating by hand" is a really bad idea as it's
platform specific -- the project now reads the values from the
`distutils.sysconfig` module, which is the settings used to compile python
(i.e. exactly what we want,) the only setting which is guessed is fortran
compiler and file extensions (which are user-configurable). I suspect it is
reimplementing a fair bit of distutils now!
* * *
The way to do this is to write your own compiler lines, and hack them into
your `setup.py`. I show an example below which works for my (very simple)
case, which has the following strucutre:
* imports
* `cythonize()` any `.pyx` files, so you only have fortran and C files.
* define a `build()` function which compiles your code:
* maybe some easy-to-change constants, like compiler names and architecture
* list up the fortran and C files
* generate the shell commands that will build the modules
* add the linker line
* run the shell commands.
* if the command was `install` and the target doesn't exist yet, build it.
* run setup (which will build the pure python sections)
* if the command was `build`, run the build now.
my implementation of this is shown below. It's designed for only one extension
module, and it recompiles all the files every time, so may require further
extension to be of more general use. Also note that I've hard coded various
unix `/`s, so if you're porting this to windows make sure you adapt or replace
with `os.path.sep`.
from distutils.core import setup
from distutils.sysconfig import get_python_inc
from Cython.Build import cythonize
import sys, os, shutil
cythonize('delaunay/sphere.pyx')
target = 'build/lib/delaunay/sphere.so'
def build():
fortran_compiler = 'gfortran'
c_compiler = 'gcc'
architecture = 'x86_64'
python_h_location = get_python_inc()
build_temp = 'build/custom_temp'
global target
try:
shutil.rmtree(build_temp)
except OSError:
pass
os.makedirs(build_temp) # if you get an error here, please ensure the build/ ...
# folder is writable by this user.
c_files = ['delaunay/sphere.c']
fortran_files = ['delaunay/stripack.f90']
c_compile_commands = []
for cf in c_files:
# use the path (sans /s), without the extension, as the object file name:
components = os.path.split(cf)
name = components[0].replace('/', '') + '.'.join(components[1].split('.')[:-1])
c_compile_commands.append(
c_compiler + ' -arch ' + architecture + ' -I' + python_h_location + ' -o ' +
build_temp + '/' + name + '.o -c ' + cf
)
fortran_compile_commands = []
for ff in fortran_files:
# prefix with f in case of name collisions with c files:
components = os.path.split(ff)
name = components[0].replace('/', '') + 'f' + '.'.join(components[1].split('.')[:-1])
fortran_compile_commands.append(
fortran_compiler + ' -arch ' + architecture + ' -o ' + build_temp +
'/' + name + '.o -c ' + ff
)
commands = c_compile_commands + fortran_compile_commands + [
fortran_compiler + ' -arch ' + architecture +
' -bundle -undefined dynamic_lookup ' + build_temp + '/*.o -o ' + target
]
for c in commands:
os.system(c)
if 'install' in sys.argv and not os.path.exists(target):
try:
os.makedirs('build/lib/delaunay')
except OSError:
# we don't care if the containing folder already exists.
pass
build()
setup(
name="delaunay",
version="0.1",
...
packages=["delaunay"]
)
if 'build' in sys.argv:
build()
This could be wrapped up into a new `Extension` class I guess, with it's own
`build_ext` command - an exercise for the advanced student ;)
|
How to do multiple string replacements in a cleaner manner? - Python
Question: What is a fast way of doing multiple string.replace? I'm trying to add spaces
to shorten english words like
he'll -> he 'll
he's -> he 's
we're -> we 're
we've -> we 've
also i'm adding spaces in between before and punctuation as such:
"his majesty" -> " his majesty "
his; majesty -> his ; majesty
Is there a faster and cleaner way to do it? It's a little too slow for the
purpose but I've been doing it this way:
def removeDoubleSpace(sentence):
sentence.replace(" ", " ")
if " " in sentence:
removeDoubleSpace(sentence)
def prepro(sentence):
sentence = sentence.replace(",", " ,")
sentence = sentence.replace(";", " ; ")
sentence = sentence.replace(":", " : ")
sentence = sentence.replace("(", " ( ")
sentence = sentence.replace("(", " ) ")
sentence = sentence.replace("‘"," ‘ ")
sentence = sentence.replace('"',' " ')
sentence = sentence.replace("'re", " 're")
sentence = sentence.replace("'s", " 's")
sentence = sentence.replace("'ll", " 'll")
sentence = removeDoubleSpace(sentence)
return sentence
Answer: You could use a few regular expressions to accomplish the same task:
import re
# Replace multiple consecutive spaces with a single space
# Example: "One Two Three Four!" -> "One Two Three Four!"
sentence = re.sub(' +', ' ', sentence)
# Surround each instance ; : ( ) ‘ and " with spaces
# Example: '"Hello;(w)o:r‘ld"' -> " Hello ; ( w ) o : r ‘ ld "
sentence = re.sub('([;:()‘"])', ' \\1 ', sentence)
# Insert a space before each instance of , 's 're and 'll
# Example: "you'll they're, we're" -> "you 'll they 're , we 're"
sentence = re.sub("(,|'s|'re|'ll)", ' \\1', sentence)
return sentence
|
GAE can't import Web.py module in virtualenv
Question: I'm trying to set up a Web.py (0.37) project in a virtualenv to run on Google
App Engine (1.7.2) but I'm getting a `ImportError: No module named web` from
the appserver.
I've installed web.py using `python setup.py install` from inside my
virtualenv and can confirm that it's installed properly because I can import
it from the python interpreter.
My actual GAE folder is outside the virtualenv but linked like so:
`ln -s ~/Development/google_appengine $VIRTUAL_ENV/google_appengine`
and added to my python path in `$VIRTUAL_ENV/lib/python2.7/site-
packages/gae.pth`
There must be an extra step I'm missing, heres the error message:
ERROR 2012-10-03 09:03:17,442 wsgi.py:203]
Traceback (most recent call last):
File "/home/sett/Development/google_appengine/google/appengine/runtime/wsgi.py", line 195, in Handle
handler = _config_handle.add_wsgi_middleware(self._LoadHandler())
File "/home/sett/Development/google_appengine/google/appengine/runtime/wsgi.py", line 239, in _LoadHandler
handler = __import__(path[0])
File "/home/sett/Development/google_appengine/google/appengine/tools/dev_appserver_import_hook.py", line 719, in Decorate
return func(self, *args, **kwargs)
File "/home/sett/Development/google_appengine/google/appengine/tools/dev_appserver_import_hook.py", line 1923, in load_module
return self.FindAndLoadModule(submodule, fullname, search_path)
File "/home/sett/Development/google_appengine/google/appengine/tools/dev_appserver_import_hook.py", line 719, in Decorate
return func(self, *args, **kwargs)
File "/home/sett/Development/google_appengine/google/appengine/tools/dev_appserver_import_hook.py", line 1787, in FindAndLoadModule
description)
File "/home/sett/Development/google_appengine/google/appengine/tools/dev_appserver_import_hook.py", line 719, in Decorate
return func(self, *args, **kwargs)
File "/home/sett/Development/google_appengine/google/appengine/tools/dev_appserver_import_hook.py", line 1730, in LoadModuleRestricted
description)
File "/home/sett/wip/rigmarolesoup/main.py", line 1, in <module>
import web
ImportError: No module named web
Answer: App engine won't let you import 3rd party modules from site-packages; you must
copy web.py into your app directory.
|
How to reuse user's raw input in other function
Question: I m making a 2D board game for python for hw.
I asked user to input a integer for the board size. for example, 7. I have
modified a bit (only show the important ones) before posting. the function is
like follows
def asksize():
while True:
ask=raw_input("Input board size: ")
try:
size=int(ask)
return size
except ValueError:
print "Please enter a integer"
Because it is variable board size, I need reuse the variable size in other
function, use it for checking user's move is valid or not, how can I reuse the
variable?
def checkmove(move):
#move is sth like eg. A1:B2
move=move.split(":") #I split it so it becomes ['A','1']['B','2']
if size>=int(move[0][1]) and int(move[0][1])>=1 and size>=int(move[1][1]) and int(move[1][1])>=1: #for example if board size is 7, this is to check whether user input is between 1 to 7 within the board
return True
else:
return False
In my checkmove function, I can't use size in my argument because it is not
defined, how can I make it workable?
Thanks
Answer: Making the variable size global is an option, but you should consider your
functions as an API, and use them on the game main bucle.
so storing the input like this:
size = asksize() #store the data on to variable called size
#then just call your check move
checkmove(x)
Anyway this is a bad exercise, its better to pass the variable through the
function inside the game code:
#definitions
def asksize():
#your code here
def checkmove(move, size):
#your code here
#game set up here
size = asksize()
#more set up stuff
#end of game set up
#Game Main code
while True: #main game bucle
#Game stuff here
checkmove(move, size)
#more game stuff
|
Automating virtualenv and Django development server startup with fabric?
Question: > **Possible Duplicate:**
> [Activate a virtualenv via fabric as deploy
> user](http://stackoverflow.com/questions/1180411/activate-a-virtualenv-via-
> fabric-as-deploy-user)
I've been advised to try and use fabric for deploying Django to a production
server, and automating tasks by using python instead of bash.
I wanted to start easily and just automate the activation of my virtualenv,
and start the Django development server in it.
I've created a file named fabfile.py:
from fabric.api import local
def activate_env():
local("source /.../expofit_env/bin/activate")
def run_local_server():
local("/.../server/manage.py runserver")
def start():
activate_env()
run_local_server()
However, when I run
fab start
i get the following message:
[localhost] local: source /.../expofit_env/bin/activate
/bin/sh: 1: source: not found
Fatal error: local() encountered an error (return code 127) while executin
'source /.../expofit_env/bin/activate'
What am I doing wrong?
* * *
**Update**
Based on Burhan Khalid's proposal, i tried the following:
....
def activate_env():
local("/bin/bash /.../expofit_env/bin/activate")
....
Running just
fab activate_env
results:
[localhost] local: /bin/bash /.../expofit_env/bin/activate
Done.
However after execution, virtualenv isn't activated. For the following code:
def start_env():
with prefix('/bin/bash /.../expofit_env/bin/activate'):
local("yolk -l")
I still get an error, as if virtualenv wasn't activated.
alan@linux ~/Desktop/expofit $ fab start_env
[localhost] local: yolk -l
/bin/sh: 1: yolk: not found
When i manually activate virtualenv, yolk workd fine:
alan@linux ~/.../expofit_env $ source bin/activate
(expofit_env)alan@linux ~/.../expofit_env $ yolk -l
DateUtils - 0.5.2 - active
Django - 1.4.1 - active
Python - 2.7.3rc2 - active development (/usr/lib/python2.7/lib-dynload)
....
* * *
**Update**
Tried a new approach from [this
question](http://stackoverflow.com/questions/1180411/activate-a-virtualenv-
via-fabric-as-deploy-user?rq=1).
from __future__ import with_statement
from fabric.api import *
from contextlib import contextmanager as _contextmanager
env.activate = 'source /.../expofit_env/bin/activate'
@_contextmanager
def virtualenv():
with prefix(env.activate):
yield
def deploy():
with virtualenv():
local('yolk -l')
Gives the same error:
[localhost] local: yolk -l
/bin/sh: 1: source: not found
Fatal error: local() encountered an error (return code 127) while executing 'yolk -l'
Aborting.
Even dough the first command passes without errors:
alan@linux ~/.../expofit_env/bin $ fab virtualenv
[servername] Executing task 'virtualenv'
Done.
**Update**
It is possible to run the `local` with a custom shell.
from fabric.api import local
def start_env():
local('source env/bin/activate',shell='/bin/bash')
However, that didn't activate the virtualenv as if it was done manually.
Answer: To use enable a virtualenv from the fab file you need to run your commands as
follow:
def task():
# do some things outside the env if needed
with prefix('source bin/activate'):
# do some stuff inside the env
pip install django-audiofield
All the commands within the with bloc will be executed inside the virtualenv
|
QtSingleApplication for PySide or PyQt
Question: Is there a Python version of the C++ class
[`QtSingleApplication`](http://doc.qt.digia.com/solutions/4/qtsingleapplication/qtsingleapplication.html)
from [Qt Solutions](http://qt.digia.com/Product/Qt-Add-Ons/Qt-Solutions-
Archive/)?
[`QtSingleApplication`](http://doc.qt.digia.com/solutions/4/qtsingleapplication/qtsingleapplication.html)
is used to make sure that there can never be more than one instance of an
application running at the same time.
Answer: Here is my own implementation. It has been tested with Python 2.7 and PySide
1.1.
It has essentially the same interface as the [C++ version of
`QtSingleApplication`](http://doc.qt.digia.com/solutions/4/qtsingleapplication/qtsingleapplication.html).
The main difference is that you must supply an application unique id to the
constructor. (The C++ version by default uses the path to the executable as a
unique id; that would not work here because the executable will most likely be
`python.exe`.)
from PySide.QtCore import *
from PySide.QtGui import *
from PySide.QtNetwork import *
class QtSingleApplication(QApplication):
messageReceived = Signal(unicode)
def __init__(self, id, *argv):
super(QtSingleApplication, self).__init__(*argv)
self._id = id
self._activationWindow = None
self._activateOnMessage = False
# Is there another instance running?
self._outSocket = QLocalSocket()
self._outSocket.connectToServer(self._id)
self._isRunning = self._outSocket.waitForConnected()
if self._isRunning:
# Yes, there is.
self._outStream = QTextStream(self._outSocket)
self._outStream.setCodec('UTF-8')
else:
# No, there isn't.
self._outSocket = None
self._outStream = None
self._inSocket = None
self._inStream = None
self._server = QLocalServer()
self._server.listen(self._id)
self._server.newConnection.connect(self._onNewConnection)
def isRunning(self):
return self._isRunning
def id(self):
return self._id
def activationWindow(self):
return self._activationWindow
def setActivationWindow(self, activationWindow, activateOnMessage = True):
self._activationWindow = activationWindow
self._activateOnMessage = activateOnMessage
def activateWindow(self):
if not self._activationWindow:
return
self._activationWindow.setWindowState(
self._activationWindow.windowState() & ~Qt.WindowMinimized)
self._activationWindow.raise_()
self._activationWindow.activateWindow()
def sendMessage(self, msg):
if not self._outStream:
return False
self._outStream << msg << '\n'
self._outStream.flush()
return self._outSocket.waitForBytesWritten()
def _onNewConnection(self):
if self._inSocket:
self._inSocket.readyRead.disconnect(self._onReadyRead)
self._inSocket = self._server.nextPendingConnection()
if not self._inSocket:
return
self._inStream = QTextStream(self._inSocket)
self._inStream.setCodec('UTF-8')
self._inSocket.readyRead.connect(self._onReadyRead)
if self._activateOnMessage:
self.activateWindow()
def _onReadyRead(self):
while True:
msg = self._inStream.readLine()
if not msg: break
self.messageReceived.emit(msg)
Here is a simple test program:
import sys
from PySide.QtGui import *
from QtSingleApplication import QtSingleApplication
appGuid = 'F3FF80BA-BA05-4277-8063-82A6DB9245A2'
app = QtSingleApplication(appGuid, sys.argv)
if app.isRunning(): sys.exit(0)
w = QWidget()
w.show()
app.setActivationWindow(w)
sys.exit(app.exec_())
|
Writing and importing custom modules/classes
Question: I've got a class that I'm trying to write called dbObject and I'm trying to
import it from a script in a different folder. My structure is as follows:
/var/www/html/py/testobj.py
/var/www/html/py/obj/dbObject.py
/var/www/html/py/obj/__init__.py
Now, `__init__.py` is an empty file. Here are the contents of dbObject.py:
class dbObject:
def __init__():
print "Constructor?"
def test():
print "Testing"
And here's the contents of testobj.py:
#!/usr/bin/python
import sys
sys.path.append("/var/www/html/py")
import obj.dbObject
db = dbObject()
When I run this, I get:
Traceback (most recent call last):
File "testobj.py", line 7, in <module>
db = dbObject()
NameError: name 'dbObject' is not defined
I'm new to Python, so I'm very confused as to what I'm doing wrong. Could
someone please point me in the right direction?
EDIT: Thanks to Martijn Pieters' answer I modified my testobj.py as follows:
#!/usr/bin/python
import sys
sys.path.append("/var/www/html/py")
sys.path.append("/var/www/html/py/dev")
from obj.dbObject import dbObject
db = dbObject()
However, now when I run it I get this error:
Traceback (most recent call last):
File "testobj.py", line 7, in <module>
db = dbObject()
TypeError: __init__() takes no arguments (1 given)
Is this referring to my **init**.py or the constructor within dbObject?
EDIT(2): Solved that one myself, the constructor must be able to take at least
one parameter - a reference to itself. Simple fix. Looks like this problem is
solved!
EDIT (Final): This is nice - I can cut out the import sys and sys.path.append
lines and it still works in this instance. Lovely.
Answer: You need to import the class from the module:
from obj.dbObject import dbObject
This adds the class `dbObject` directly to your local namespace.
Your statement `import obj.dbObject` adds the name `obj` to the local
namespace, so you could also do this instead:
db = obj.dbObject.dbObject()
because `obj.dbObject` is the `dbObject.py` module in your `obj` package
directory.
|
Is it possible to use the Yahoo Query Language to download historical financial data?
Question: I've used the Yahoo Finance site to download historical data, using queries
like this:
http://ichart.finance.yahoo.com/table.csv?s=AAPL&c=1962
and the accompanying Python code:
import urllib.request
with open("data.csv", "wb") as w:
url = "http://ichart.finance.yahoo.com/table.csv?s=AAPL&c=1962"
r = urllib.request.urlopen(url).read()
w.write(r)
I've also used the Yahoo Query Language to download pseudo-realtime data (i.e.
data delayed by a few minutes) with queries like this:
http://query.yahooapis.com/v1/public/yql?q=select%20*%20from%20yahoo.finance.quotes%20where%20symbol%20in%20(%22AAPL%22)&env=store://datatables.org/alltableswithkeys
However, I can't find documentation on how to download historical data (as
shown in the first query) using the YQL (as shown in the second query). I'd
like to do this before the tables returned by the YQL contain much more data
than simply opening/closing prices, volume, etc.
Is there a way to download historical data using the YQL in such a way that it
contains the same depth of detail as the pseudo-realtime data?
Answer: Unfortunately, the YQL table `yahoo.finance.historicaldata` contains the same
fields as the CSV files, specifically the opening price, closing price, high,
low, volume, etc. To download this data using YQL, this is an example of the
proper query:
select * from yahoo.finance.historicaldata where symbol = "IBM" and startDate = "2012-01-01" and endDate = "2012-01-11"
|
How to create REST API application using python Bottle framework and how to deploy it on apache server?
Question: I want to create one sample application for api's using python Bottle
framework, I want to deploy that application on apache server as well, I use
following sample code,
from bottle import route, run, template
@route('/hello/:name')
def index(name='World'):
return template('<b>Hello {{name}}</b>!', name=name)
@route('/events/:id', method='GET')
def get_event(id):
return dict(name = 'Event ' + str(id))
run(host='localhost', port=8082)
by using above code, How I can create sample application and how I can deploy
that sample application on server. How can achieve this?
Answer: [**@phihag**](http://stackoverflow.com/users/35070/phihag), go through these
articles by Miguel Grinberg,
[@miguelgrinberg](http://twitter.com/miguelgrinberg) ~
<http://blog.miguelgrinberg.com/category/REST>
Start with this article, "**[Designing a RESTful API with Python and
Flask](http://blog.miguelgrinberg.com/post/designing-a-restful-api-with-
python-and-flask)** " ~ and if need be install Flask, go through the steps.
Then re-write the application in Bottle. Bottle is a simple framework to use
and is so close to Flask I re-wrote the code reading through the example in
Bottle. There is a more [detailed
tutorial](http://blog.miguelgrinberg.com/post/designing-a-restful-api-using-
flask-restful) that you can look at once you have the basics.
It's worth the effort.
|
Python sum() returns negative value because the sum is too large for 32bit integer
Question:
x = [1, 2, 3, ... ]
y = sum(x)
The sum of `x` is 2165496761, which is larger than the limit of 32bit integer
So `sum(x)` returns -2129470535.
How can I get the correct value by converting it to long integer?
Here is my import list:
import math, csv, sys, re, time, datetime, pickle, os, gzip
from numpy import *
Answer: Twenty quatloos says you're using `numpy`'s sum function:
>>> sum(xrange(10**7))
49999995000000L
>>> from numpy import sum
>>> sum(xrange(10**7))
-2014260032
So I'd bet you did `from numpy import *` or are using some interface which
does the equivalent.
To verify this, try
print type(sum(x))
On the example posted elsewhere in this thread:
>>> sum([721832253, 721832254, 721832254])
-2129470535
>>> type(sum([721832253, 721832254, 721832254]))
<type 'numpy.int32'>
Edit: somebody owes me twenty quatloos! Either don't use the star import
(best), manually set the `dtype`:
>>> sum([721832253, 721832254, 721832254],dtype=object)
2165496761L
or refer to the builtin `sum` explicitly (possibly giving it a more convenient
binding):
>>> __builtins__.sum([721832253, 721832254, 721832254])
2165496761L
|
easy_install conflict for python2.4 and python2.7
Question: I have installed python under /opt/python2.7.1/ on CentOS machine which has
already python2.4 and configure it to run python2.7 default.
However, when I write 'easy_install' it raises error like
Traceback (most recent call last):
File "/opt/python2.7.1/bin/easy_install", line 5, in ?
from pkg_resources import load_entry_point
File "/usr/lib/python2.4/site-packages/pkg_resources.py", line 2482, in ?
for dist in working_set.resolve(
File "/usr/lib/python2.4/site-packages/pkg_resources.py", line 483, in resolve
raise DistributionNotFound(req) # XXX put more info here
pkg_resources.DistributionNotFound: setuptools==0.6c11
I think `easy_install` under `/usr/bin/` links to python2.4. How can I run
`/opt/python2.7.1/bin/easy_install` default?
For $PATH:
/opt/python2.7.1/bin:/usr/devs/bin:/usr/local/bin:/bin:/usr/bin:/home/ops/bin
For $LD_LIBRARY_PATH:
/opt/python2.7.1/lib:
For easy_install:
Traceback (most recent call last):
File "/opt/python2.7.1/bin/easy_install", line 5, in ?
from pkg_resources import load_entry_point
File "/usr/lib/python2.4/site-packages/pkg_resources.py", line 2482, in ?
for dist in working_set.resolve(
File "/usr/lib/python2.4/site-packages/pkg_resources.py", line 483, in resolve
raise DistributionNotFound(req) # XXX put more info here
pkg_resources.DistributionNotFound: setuptools==0.6c11
Answer: You have to make use of
[virtualenv](http://www.virtualenv.org/en/latest/index.html) to get things
working properly, and without worries in systems with more than one Python
version.
Actually, it is quite a help even in system qwith a single Python version, if
you have muliple Python apps running.
Visrtualenv will not only take care of setting up all the appropriate
environment variables for you to use one Python or another, as it will allow
you to use use a separate environment where you can safely "easy_install"
Python 2.4 modules without conflicting with CentOS .rpm packages of those same
modules.
|
Get absolute path of file why traversing through another directory
Question: I have a small snipped in python which intends to traverse through all the
directory , subdirectory and manitain a list of absolute path of all the files
.
code:
import os , pickle
root="/home/me/programs/"
l = [] #Will have list of all the files parsed through
for dname,subdirlist,flist in os.walk(root):
for fname in flist:
l.append(os.path.abspath(fname))
Even though i am parsing through all the files , my output is prefixing
`/home/me/programs/` irrespective of the actual absolute path.
For example, instead of having
`'/home/me/programs/cpp/sample/test.c'`
i will have `'/home/me/programs/test.c'`
How do i fix this problem ?
Answer: As mentioned in the [`os.walk`
doc](http://docs.python.org/library/os.html#os.walk), you'll have to join the
root path to your fname to get the absolute path :
import os , pickle
root="/home/me/programs/"
l = [] #Will have list of all the files parsed through
for dname,subdirlist,flist in os.walk(root):
for fname in flist:
l.append(os.path.join(dname, fname))
|
DNS server client communication protocol
Question: I need to write a paper on how DNS works and build a small but functional DNS
server in python.
I have a simple UDP socket server that opens a thread when a packet is
received like this:
while 1:
try:
stream, addr = serversocket.recvfrom(buffr)
threading.Thread(target=handler, args=(stream, addr, threading.activeCount(),)).start()
except:
exc_type, exc_value, exc_traceback = sys.exc_info()
except_catch(exc_type.__name__, exc_value, exc_traceback, threading.current_thread().name)
The handler function simply tries to find the record requested in memory and
if it does not it will execute another function that runs a dns query on
another server to fetch the record if he does not have it. This is somewhat of
a fail-safe and where my problem is.
def dnsrn(ip, type):
try:
mkr = dns.resolver.Resolver()
mkr.nameservers = ['192.168.0.1']
res = mkr.query(ip, type)
for rdata in res:
return rdata.address # this works for A records
# to do for other types of records
except:
exc_type, exc_value, exc_traceback = sys.exc_info()
except_catch(exc_type.__name__, exc_value, exc_traceback, threading.current_thread().name)
**I have not yet finished it as you can see but I already have a problem.
Sometimes, this function will hand and the thread will never finish without it
giving any error what so ever in the error log. I have tested and the error
log should capture all errors thrown by the child. I have a simple client that
is programmed to send a random request out a lit of presets every set time and
there seems to be no pattern to when the child hangs. After about 24 hours of
testing I'm left with about 1-3 zombie threads.**
In case you are wondering this is what the exception function looks like:
def except_catch(type, value, track, thread=None):
if type != "SystemExit":
import traceback
rawreport = traceback.format_exception(type, value, track)
report = "\n" . join(rawreport)
errorlog = open(error_log_path + "/errors.log", "a")
if thread != None:
errorlog.write("Exception in thread: " + thread + "\n\n")
errorlog.write(("%s\n" + "-" * 30 + "\n\n") % report)
errorlog.close()
sys.excepthook = except_catch
Answer: I would check the RFC as this is the exact specification of the protocol. The
problem with DNS is, that there is more than one RFC. For a simple start, I
would check [RFC 1035](http://tools.ietf.org/html/rfc1035) which contains the
basics. If you need advanced functionality, check the other related RFCs.
|
Append xml to xml using python.I have two xml files which i need to merge .so is there anyway i can merge both files
Question: can anybody tell me how to append xml files using python
this is my file1.xml
<?xml version="1.0"?>
<addressbook>
<person>
<name>Eric Idle</name>
<phone type='fix'>999-999-999</phone>
<phone type='mobile'>555-555-555</phone>
<address>
<street>12, spam road</street>
<city>London</city>
<zip>H4B 1X3</zip>
</address>
</person>
</addressbook>
and i want to append it to another xml file
<?xml version="1.0"?>
<note>
<to>Tove</to>
<from>Jani</from>
<heading>Reminder</heading>
<body>Don't forget me this weekend!</body>
</note>
Is there any module which can do this for me...
and the output i needed is :
<addressbook>
<person>
<name>Eric Idle</name>
<phone type='fix'>999-999-999</phone>
<phone type='mobile'>555-555-555</phone>
<address>
<street>12, spam road</street>
<city>London</city>
<zip>H4B 1X3</zip>
</address>
</person>
<note>
<to>Tove</to>
<from>Jani</from>
<heading>Reminder</heading>
<body>Don't forget me this weekend!</body>
</note>
</addressbook>
And for now i need to read xml from files but later i need to get the xml
response from server and the convert it into one xml file .So please if any
one know that to it will help me alot......
Answer: **EDIT** : Removed old answer as the question changed considerably.
Using lxml:
addressbook_xml = """<?xml version="1.0"?>
<addressbook>
<person>
<name>Eric Idle</name>
<phone type='fix'>999-999-999</phone>
<phone type='mobile'>555-555-555</phone>
<address>
<street>12, spam road</street>
<city>London</city>
<zip>H4B 1X3</zip>
</address>
</person>
</addressbook>"""
note_xml = """<?xml version="1.0"?>
<note>
<to>Tove</to>
<from>Jani</from>
<heading>Reminder</heading>
<body>Don't forget me this weekend!</body>
</note>
"""
from lxml import etree
# XML strings to etree
addressbook_root = etree.fromstring(addressbook_xml)
note_root = etree.fromstring(note_xml)
# append the note
addressbook_root.append(note_root)
# print the new addressbook XML document
print etree.tostring(addressbook_root)
|
PrintWriter flush not working?
Question: I'm trying to get the following code working so that I can use it somewhere
else.
Effectively, it (is supposed to) start another process, run python in it, and
feed python some commands. However, in practice, unless I close the stream to
that process, the the python commands are never sent. I thought flush() was
supposed to force this to happen, but it does not appear to be working. Could
anyone provide any insight as to why flush() may not be working and what I
could do to avoid this? Thanks.
Note that if I call close() the command is sent. However, I want to be able to
send more commands after this one command, so using close() here seems
unacceptable. (I'll eventually close() everything)
import java.io.BufferedWriter;
import java.io.IOException;
import java.io.InputStream;
import java.io.InputStreamReader;
import java.io.OutputStream;
import java.io.OutputStreamWriter;
import java.io.PrintWriter;
import java.util.Scanner;
public class Foo {
public static void main(String[] args) throws IOException {
Process cmd = Runtime.getRuntime().exec("python");
InputStream inStream = cmd.getInputStream();
Thread stdout = new Thread(new stdOutReader(inStream));
stdout.start();
InputStream errStream = cmd.getErrorStream();
Thread stderr = new Thread(new stdOutReader(errStream));
stderr.start();
OutputStream outStream = cmd.getOutputStream();
OutputStreamWriter os = new OutputStreamWriter(outStream);
PrintWriter pWriter = new PrintWriter(outStream, true);
pWriter.println("print \"Testing..\"");
pWriter.flush();
int x = 0;
while (x < 100){
//Do stuff here (will not be an infinite loop in actual code)
}
pWriter.close();
}
private static class stdOutReader implements Runnable{
InputStream inStream;
public stdOutReader(InputStream inStream){
this.inStream = inStream;
}
public void run() {
InputStreamReader reader = new InputStreamReader(this.inStream);
Scanner scan = new Scanner(reader);
while (scan.hasNext()) {
System.out.println(scan.next());
System.out.flush();
}
}
}
}
Answer: Consider using [Apache Commons
Executor](http://commons.apache.org/exec/index.html) instead of using the
`Runtime.exec()` API directly.
|
Python Requests and persistent sessions
Question: I am using the [requests](http://docs.python-requests.org/en/latest/) module
(version 0.10.0 with Python 2.5). I have figured out how to submit data to a
login form on a website and retrieve the session key, but I can't see an
obvious way to use this session key in subsequent requests. Can someone fill
in the ellipsis in the code below or suggest another approach?
>>> import requests
>>> login_data = {'formPosted':'1', 'login_email':'[email protected]', 'password':'pw'}
>>> r = requests.post('https://localhost/login.py', login_data)
>>>
>>> r.text
u'You are being redirected <a href="profilePage?_ck=1349394964">here</a>'
>>> r.cookies
{'session_id_myapp': '127-0-0-1-825ff22a-6ed1-453b-aebc-5d3cf2987065'}
>>>
>>> r2 = requests.get('https://localhost/profile_data.json', ...)
Answer: You can easily create a persistent session using:
s = requests.session()
After that, continue with your requests as you would:
s.post('https://localhost/login.py', login_data)
#logged in! cookies saved for future requests.
r2 = s.get('https://localhost/profile_data.json', ...)
#cookies sent automatically!
#do whatever, s will keep your cookies intact :)
For more about sessions: <http://docs.python-
requests.org/en/latest/user/advanced/#session-objects>
|
Post-EasyTether, PDANet Tethering Samsung Galaxy 4g to Mac OS X 10.7.4 to Implement Python
Question: I'm using Mac OS X Version 10.7.4 and Python 3.2.3. I've read through many of
the equally frustrated posts on Stack Overflow, this one was especially useful
in helping me delete EasyTether after it didn't work, and turns out was
blocking PDANet from working:
[mac os x 10.6.6 and "adb devices" fails to list android
devices](http://stackoverflow.com/questions/4680637/mac-os-x-10-6-6-and-adb-
devices-fails-to-list-android-devices)
I'm using Paul Ferrill's "Pro Android Python with SL4A" and for the past 4
hours I've just wanted to be able to type the following in my Mac's IDLE
session:
>>>import android
>>>droid = android.Android()
>>>droid.makeToast("Hello Android from Mac")
I'm pretty stymied at this point. I've allowed USB debugging on my Samsung
Galaxy 4g, I finally have the PDANet software working, but I have nothing to
show for it. I've watched a bunch of Youtube tutorials, this one was helpful
for installing PDANet:
<http://www.youtube.com/watch?v=yR9GANNKUgo>
A lot of other people had similar trouble with EasyTether, but now that I have
PDANet working, I still can't seem to get this code to work. Right now, my I
have the following:
Python 3.2.3 Type "copyright", "credits" or "license()" for more information.
> > > import android
Traceback (most recent call last):
File "", line 1, in
import android
ImportError: No module named android
> > > I would be so very thankful for any help you can provide.
**Correction**
I understand that the reason the code throws an error is that the android
module is not found on my computer. I'm simply wondering how I can get my Mac
to connect with my Samsung Galaxy such that I can write the above code and
have the file android.py that is on my android register with my script on my
Mac, such that the program works.
Answer: I'm not sure if that book is great for Python 3. There is a Python3
APK(http://code.google.com/p/python-for-
android/downloads/detail?name=Python3ForAndroid_r6.apk), but the other one,
the standard PythonForAndroid is 2.6(?) based. You need to use the same
version of python across both your android device and your local machine for
what you're trying to do. I'm not sure which Python 3 ve
When I was playing with this and the same book, I had to install the same
version of python on my local machine that was used in the APK I installed on
my device. It was still a lot of screwing around to get it to work and wasn't
really worth the effort in the end.
However, I found that just pushing the script across and instantly running it
was way easier than trying to play with IDLE remotely. This is now how I
rapidly prototype any Android apps I'm planning to work on.
|
python epoll and nonblocking
Question: simple client-server socket studying code,the server-end is:
import socket,select,time
s = socket.socket()
host = socket.gethostname()
port = 1234
s.bind((host,port))
s.listen(50)
s.setblocking(0) # (1)
fdmap = {s.fileno():s}
p = select.epoll()
p.register(s)
while True:
events = p.poll()
for fd,event in events:
if fd is s.fileno():
c,addr = s.accept()
c.setblocking(0) #(2)
print('Got connection from: ',addr)
p.register(c)
fdmap[c.fileno()] = c
elif event & select.EPOLLIN:
data = fdmap[fd].recv(1024)
if not data:
print('disconnected')
p.unregister(fd)
del fdmap[fd]
else:
print(data)
and the client-end is
import socket,time
s = socket.socket()
host = socket.gethostname()
port = 1234
s.connect((host,port))
print(s.send(b'hello server'))
My questions are:
1.AFAIK in the IO-multiplexing model,epoll.poll would block until one socket
become available,so when operates on it,it shouldn't be block(should return
directly),then why we should call setblocking(0) in (1),(2),what's the
purpose? I tried put them off,it still works
2.when running,the client-end can be slow,it outputs 12(which is the bytes it
send to server) after about 1s,I profiling it by use time.time() one by one
statement,then found that the s.connect((host,port)) usually take about
1s,where am i wrong?(This happens on poll/epoll,when use select,the client-end
goes very fast)
Answer: If you check the
[documentation](http://docs.python.org/library/select.html#select.epoll.poll)
you will see that the epoll `poll` function takes a `timeout` parameter, which
defaults to `-1` which means wait indefinitely. If you set the timeout to zero
it will return immediately.
As for the delay in `connect` it's probably because `connect` has to do a DNS
lookup of the hostname to find the IP address.
|
how to launch a command window from Python
Question: I'd like to use Python 2.6 on Windows to launch several **separate** command
windows, each running their own Python script. The purpose is: these are
clients, and I'm trying to load up the server with requests from multiple
quasi-independent clients.
I don't need to communicate with the client during or after the run, but I do
need to send each a different commmandline arg, and I'd like each client's
output to scroll in its own "console".
From the DOS command line, the "start" command does what I'd like. I can
either:
start perf_test.py 2
or
start cmd /c perf_test.py 3
or
start cmd /c python perf_test.py 4
(These will work for you if you have your "file associations" setup correctly
for *.py files. There are other threads on that, if you need help. Or, use
full paths to the python exe and/or your script.)
My challenge is: How do I get the same effect from Python?
Using `subprocess` library, I've tried variations like this:
from subprocess import *
p = Popen(["perf_test.py", "4"], shell=True, stdin=PIPE)
But even with `shell=True`, the output is commingled in the window I'm already
running in. Adding `stdout=PIPE` stops that, but then I have to read
`p.stdout` or use `p.communicate()`. Adding "cmd" to the Popen gets
approximately the same:
p = Popen(["cmd", "/c", "perf_test.py", "4"], shell=True, stdin=PIPE)
None of the above achieve the effect I'm looking for, which is: "**pop open a
new, distinct window for this script, and watch its output scroll by in its
own console** " (because I really want to run N of these clients in parallel).
One other thing I turned to _almost_ works, too.
import os
os.startfile("perf_test.py")
This returns immediately, and an actual dosbox pops up. Yay! Success! That is,
until I try to add an argument. This fails:
os.startfile("perf_test.py 5")
with error "The system cannot find the file specified"... because it is adding
"[SPACE]5" to the filename. (The purpose of the argument is that each
"perf_test" needs to have an assigned ID, so that they hit the server as
different instances.)
Other approaches I've considered, and really don't like for various reasons:
* Run each "perf_test" in its own thread. (But I really want to see the output each in its own console.)
* Make my own pseudo-consoles with Tk. (Figure I'll just hit different threading problems there.)
* Dynamically write a .BAT file on the fly with the lines "start perf_test.py 1", "start perf_test.py 2", etc., then launch that .BAT file with `Popen` or `startfile`.
I expect the last will work... and I guess is my last resort, if I can't get a
Python script to do it directly.
Thanks for any input / insights!
Answer: You can use:
import os
os.system("start python perf_test.py 5")
|
python: combine values in one column on the basis of ids in another column
Question: I need to combine values in second column of a tab delimited file based on the
ids in first column. The example is given below. What is the fastest way to do
this. I can do it using for loop, going through each line, but I am sure there
is some smart way to do it, which I am not aware of.
596230 Other postop infection
596230 Disseminated candidiasis
596230 Int inf clstrdium dfcile
596230 Pressure ulcer, site NOS
2846079 Schizophrenia NOS-unspec
7800713 CHF NOS
7800713 Chr airway obstruct NEC
7800713 Polymyalgia rheumatica
7800713 DMII wo cmp nt st uncntr
into
596230 Other postop infection, Disseminated candidiasis, Int inf clstrdium dfcile, Pressure ulcer, site NOS
2846079 Schizophrenia NOS-unspec
7800713 CHF NOS, Chr airway obstruct NEC, Polymyalgia rheumatica, DMII wo cmp nt st uncntr
Answer: Assuming you have your text in a file:
from collections import defaultdict
items = defaultdict(list)
with open("myfile.txt") as infile:
for line in file:
id, text = line.rstrip().split("\t")
items[id].append(text)
for id in items:
print id + "\t" + ", ".join(items[id])
This does not keep the original order of your `id`s, but it does keep the
order of the texts.
|
Python TypeError when using class (wx.Python)
Question: This program is that wx.textctrl is written "clicked" when button is clicked.
This code runs without error.
import wx
class Mainwindow(wx.Frame):
def __init__(self, parent, id, title):
wx.Frame.__init__(self, parent, id, title, size=(300, 300))
panel = wx.Panel(self, -1)
vbox = wx.BoxSizer(wx.VERTICAL)
hbox1 = wx.BoxSizer(wx.HORIZONTAL)
btn = wx.Button(panel, -1, 'OK', size=(70, 30))
btn.Bind(wx.EVT_BUTTON, self.click_btn) #line 12
hbox1.Add(btn, 0)
vbox.Add(hbox1, 0)
hbox2 = wx.BoxSizer(wx.HORIZONTAL)
self.tc = wx.TextCtrl(panel, -1, style=wx.TE_MULTILINE)
hbox2.Add(self.tc, 1, wx.EXPAND)
vbox.Add(hbox2, 1, wx.EXPAND)
panel.SetSizer(vbox)
self.Centre()
self.Show(True)
def click_btn(self, event): #line 27
self.tc.WriteText("clicked\n") #line 28
if __name__=="__main__":
app = wx.App()
Mainwindow(None, -1, u"sample")
app.MainLoop()
But if this code change in this way, it gets error.
change to line 12.
btn.Bind(wx.EVT_BUTTON, Click_btn.click_btn)
change to line 27 and 28.
class Click_btn:
def click_btn(self, event):
self.tc.WriteText("clicked\n")
The error is: Typeerror: unbound method click_btn() must be called with
Click_btn instance as first argument (got CommandEvent instance instead)
I don't know how to cope with this error.
*Postscript
I read answer,and this code change. But it don't run...
change to line 12.
button = Click_btn()
btn.Bind(wx.EVT_BUTTON, button.click_btn)
change to line 27 and 28.
class Click_btn(Mainwindow):
def click_btn(self, event):
Mainwindow.tc.WriteText("clicked\n")
Please teach point that I should change.
Answer:
class Click_btn:
@classmethod
def click_btn(cls, event):
cls.tc.WriteText("clicked\n") #this will probably break now
this will allow you to call it on the class rather than an instance of the
class
the class is `Click_btn`
an instance would be `btn = Click_btn()` (btn is the instance of Click_btn)
|
Merging similar dictionaries in a list together
Question: New to python here. I've been pulling my hair for hours and still can't figure
this out.
I have a list of dictionaries:
[ {'FX0XST001.MID5': '195', 'Name': 'Firmicutes', 'Taxonomy ID': '1239', 'Type': 'phylum'}
{'FX0XST001.MID13': '4929', 'Name': 'Firmicutes', 'Taxonomy ID': '1239','Type': 'phylum'},
{'FX0XST001.MID6': '826', 'Name': 'Firmicutes', 'Taxonomy ID': '1239', 'Type': 'phylum'},
.
.
.
.
{'FX0XST001.MID6': '125', 'Name': 'Acidobacteria', 'Taxonomy ID': '57723', 'Type': 'phylum'}
{'FX0XST001.MID25': '70', 'Name': 'Acidobacteria', 'Taxonomy ID': '57723', 'Type': 'phylum'}
{'FX0XST001.MID40': '40', 'Name': 'Acidobacteria', 'Taxonomy ID': '57723', 'Type': 'phylum'} ]
I want to merge the dictionaries in the list based on their Type, Name, and
Taxonomy ID
[ {'FX0XST001.MID5': '195', 'FX0XST001.MID13': '4929', 'FX0XST001.MID6': '826', 'Name': 'Firmicutes', 'Taxonomy ID': '1239', 'Type': 'phylum'}
.
.
.
.
{'FX0XST001.MID6': '125', 'FX0XST001.MID25': '70', 'FX0XST001.MID40': '40', 'Name': 'Acidobacteria', 'Taxonomy ID': '57723', 'Type': 'phylum'}]
I have the data structure setup like this because I need to write the data to
CSV using csv.DictWriter later.
Would anyone kindly point me to the right direction?
Answer: You can use the groupby function for this:
<http://docs.python.org/library/itertools.html#itertools.groupby>
from itertools import groupby
keyfunc = lambda row : (row['Type'], row['Taxonomy ID'], row['Name'])
result = []
data = sorted(data, key=keyfunc)
for k, g in groupby(data, keyfunc):
# you can either add the matching rows to the item so you end up with what you wanted
item = {}
for row in g:
item.update(row)
result.append(item)
# or you could just add the matched rows as subitems to a parent dictionary
# which might come in handy if you need to work with just the parts that are
# different
item = {'Type': k[0], 'Taxonomy ID' : k[1], 'Name' : k[2], 'matches': [])
for row in g:
del row['Type']
del row['Taxonomy ID']
del row['Name']
item['matches'].append(row)
result.append(item)
|
Modulo operator in Python
Question: What does modulo in the following piece of code do?
from math import *
3.14 % 2 * pi
How do we calculate modulo on a floating point number?
Answer: Mathematically, the modulo operator can be represented as:
a % b = c
a - n*b = c
Where `n` is an integer that makes `c` as small as possible, but positive.
In this case:
3.14 % 2
= 3.14 - 1 * 2
= 1.14
Also, `3.14 % 2 * pi` is interpreted as `(3.14 % 2) * pi`. I'm not sure if you
meant to write `3.14 % (2 * pi)` (in either case, the algorithm is the same.
Just subtract/add until the number is as small as possible).
|
Heroku Django: Redirect all requests for www. to root domain
Question: I need to redirect all requests coming from `www.mysite.com` to `mysite.com`
I have found the [solution in
rails](http://blog.dynamic50.com/2011/02/22/redirect-all-requests-for-www-to-
root-domain-with-heroku/), but how can I do that in django/python?
The only solution I could fine, which was posted by a moderator on GoDaddy was
the above. Seems like I cannot resolve this kind of problem through the DNS
Manager of GoDaddy.
Any hints or thoughts?
Thanks in advance.
Answer: Solved whit this:
from django.http import HttpResponsePermanentRedirect
class WWWRedirectMiddleware(object):
def process_request(self, request):
if request.META['HTTP_HOST'].startswith('www.'):
return HttpResponsePermanentRedirect('http://mysite.com')
|
Use Python to Optimally find Top 10 recently created files
Question: I am trying to find a optimal way of extracting most recently, say 10, created
files from a directory tree using Python. I've found a number[1, 2] of
interesting solutions, however, they only involved a single file.
├── d1
│ ├── d1-1
│ ├── d1-1
:
├── d2
│ ├── d2-1
│ └── d2-2
│ │ ├── f1.xxx
: :
│ │ ├── fn.xxx
├── d3
│ ├── d3-1
:
:
The only way I can think of doing that, at the moment, is iteratively
appending results by looping through the same tree until I have desired 10
results; the problem with this approach is that it will clearly be time
consuming... especially that my directory trees may be huge. An alternative
solution I thought about involves parsing an entire directory tree and
generating file name paths with their corresponding creation or modification
dates and then possibly use that 'index' file to get top 10 recent files. A
database would have perhaps been useful here, however, it's not an option at
the moment.
Does anyone know of an optimal way of achieving this?
[1] [Python return filepath/filename of most recent csv file stored in
directory](http://stackoverflow.com/q/11900038/664424)
[2] [Find the most recent file in a directory without reading all the contents
of it](http://stackoverflow.com/q/4709968/664424)
Answer: You could write a generator function to return the creation time and the
filename, and use the `heapq` module to automatically keep track of the latest
'n' entries rather efficiently - example:
import os
import heapq
def iterfiles(root):
for base, dirs, files in os.walk(root):
for filename in files:
fullname = os.path.join(base, filename)
yield os.stat(fullname).st_ctime, fullname
print heapq.nlargest(10, iterfiles('some path here'))
Just an aside - you may have to handle an `IOError` (a try/except around the
yield) if permissions aren't available to stat the file.
|
runserver must be manually restarted after error in models.py
Question: I'm following the book The Definitive Guide to Django and one thing I've
started noticing is that whenever I make a single error in my models file, the
server just hangs and is not automatically restarted when the error is fixed.
Here's an example: I save the file with a line like this
email = models.EmailField(blank=Tru)
Which raises the obvious error and stack trace
Validating models...
Unhandled exception in thread started by <bound method Command.inner_run of <django.core.management.commands.runserver.Command object at 0x00000000025B0400>>
Traceback (most recent call last):
File "C:\Python27\lib\site-packages\django\core\management\commands\runserver.py", line 91, in inner_run
self.validate(display_num_errors=True)
File "C:\Python27\lib\site-packages\django\core\management\base.py", line 266, in validate
num_errors = get_validation_errors(s, app)
File "C:\Python27\lib\site-packages\django\core\management\validation.py", line 30, in get_validation_errors
for (app_name, error) in get_app_errors().items():
File "C:\Python27\lib\site-packages\django\db\models\loading.py", line 158, in get_app_errors
self._populate()
File "C:\Python27\lib\site-packages\django\db\models\loading.py", line 64, in _populate
self.load_app(app_name, True)
File "C:\Python27\lib\site-packages\django\db\models\loading.py", line 88, in load_app
models = import_module('.models', app_name)
File "C:\Python27\lib\site-packages\django\utils\importlib.py", line 35, in import_module
__import__(name)
File "C:\....\models.py", line 17, in <module>
class Author(models.Model):
File "C:\...\models.py", line 20, in Author
email = models.EmailField(blank=Tru)
NameError: name 'Tru' is not defined
Now, if I change `Tru` to `True`, the server does not restart. Is this
intentional? Or is there something wrong with my application? I've just
started learning Django so I have no idea if this is common behaviour.
I'm on Windows, running Python 2.7.3 and Django 1.4.1.
Answer: Not just you- I also experience this on occasion.
Although the development server is usually pretty good about restarting after
code changes, some particularly egregious errors (especially in your
`models.py`) can sometimes cause it to hang. Just need to terminate it
(`Ctrl+C`), restart it, and continue along your merry way.
|
Unable to execute Django runserver and no suggested solution seems to work
Question: I've run Django servers on localhost before and have never run into this
problem. I'm desperately trying to figure out what I've done wrong.
I'm using Django 1.4 with Python 2.7 on Ubuntu 12.04.
As far as I can tell I've configured everything correctly - I'm actually using
another functional Django project I built as a go-by.
If I run the following command (or any recommended variation thereof) I
receive an error.
django-admin.py runserver localhost:8000
Here is the error:
ImportError: Settings cannot be imported, because environment variable DJANGO_SETTINGS_MODULE is undefined.
Can someone please enlighten me as to why this error is occurring, how to fix
it and why it doesn't happen with my other Django project?!?
I've found many posts regarding this problem just by doing some quick Google
searches, but none of the suggested solutions have helped - nor do I truly
understand them.
Answer: I'm pretty sure you're supposed to run
manage.py runserver
from inside your project directory. It automatically loads your settings.py,
etc.
From the [Django docs](https://docs.djangoproject.com/en/dev/ref/django-
admin/):
> Generally, when working on a single Django project, it’s easier to use
> manage.py. Use django-admin.py with DJANGO_SETTINGS_MODULE, or the
> --settings command line option, if you need to switch between multiple
> Django settings files
|
Weird select error in python
Question: Ok, so I have Python 2.5 and Windows XP. I was using select.select with a
socket object. I tried it again and again, but whenever I run it, the thread
it is in gives me an error like select.error(9, "Bad file descriptor"). The
code is something like this:
import socket, select
s = socket.socket()
s.bind((socket.gethostbyname(socket.gethostname()), 1312))
s.listen(5)
inputs = [s]
outputs = []
while True:
r, w, e = select.select(inputs, outputs, inputs)
for sock in r:
if sock is s:
inputs.append(s.accept()[0])
else:
print s
print s.recv(1024)
Any info would be appreciated. Thanks!
Answer: 1. You called `select.select` with no arguments. It should be something like: `select.select(inputs, outputs, [])`.
2. In the `else` you need to use `sock`, not `s` (the server).
3. Once the peer disconnects from a previously connected socket, you should remove it from the `inputs` list. You can know the peer has disconnected if `sock.recv()` returns an empty string or raises a `socket.error` exception. If you don't do this, you might end up feeding an invalid socket descriptor to `select.select`, causing the error you talked about.
|
How to remove accents from strings using Python (encoding parameter)?
Question: I'm trying to remove accents from data in a csv file. So I use the
remove_accents function (See below) but for that I need to encode my csv files
in utf-8. But I've got the error `'encoding' is an invalid keyword argument
for this function`
I've seen that I may have to use Python3 and then execute python3
./myscript.py? Is this the right way to do it ? Or is there another way to
remove accents wihtout having to install python3 ? Any help would be much
appreciated
#!/usr/bin/env python
import re
import string
import csv
import unicodedata
def remove_accents(data):
return ''.join(x for x in unicodedata.normalize('NFKD', data) if \
unicodedata.category(x)[0] == 'L').lower()
reader=csv.reader(open('infile.csv', 'r', encoding='utf-8'), delimiter='\t')
writer=csv.writer(open('outfile.csv', 'w', encoding='utf-8'), delimiter=',')
for line in reader:
if line[0] != '':
person=re.split(' ',line[0])
first_name = person[0].strip().upper()
first_name1=unicode(first_name)
first_name2=remove_accents(first_name1)
if len(person) == 2:
last_name=person[1].strip().upper()
line[0]=last_name
line[15]=first_name2
writer.writerow(line)
Answer: You need to use
[`codecs.open()`](http://docs.python.org/library/codecs.html#codecs.open) if
you want to be able to specify an encoding. Also,
[`unidecode`](http://pypi.python.org/pypi/Unidecode/).
|
Issues with pyinstaller
Question: I have created a working GUI program (using tkinter), but when I try to
compile it using pyinstaller (py2exe only works for python 2.6 and I used 2.7
for the program), it doesn't work. I have 2 files: program.py, and data.xml.
The program uses the xml document to retrieve information and display it to
the window. I have looked all over, but no one seems to have had a similar
problem, and the pyinstaller documentation is useless. the command I used was
python pyinstaller.py -w -mdata.xml -nProgram program.py
It appears to make the spec file fine, but generates an error with a large
traceback upon build:
pyinstaller.utils.winmanifest.invalidManifestError: Invalid root element <items> - has to be one of <assembly>, <assemblyBinding>, <configuration>, <dependentAssembly>
and quits the build process. This is the first time I have tried to build an
executable for a project, so I'm kind of shooting in the dark here. Did I
forget to do something, or did I just find a bug in pyinstaller's program?
Answer: Normally I wouldn't answer my own question, but I have solved the issue and I
think others should know about this. When creating your program and using an
xml with it, you must have the root tag (the first one) as `<assembly>`. Not
sure why, but it works when I do that. also, don't forget to use the
`--hidden-import=Module` command if you imported anything into your program.
|
python "import media" didn't work but there was "media.py"
Question: I read a book to learn python programming, it showed the code :
import media
So I downloaded `gwpy-code.zip` from the link
<http://pragprog.com/titles/gwpy/source_code> and installed
`PyGraphics-2.0.win32.exe` . In the path `C:\Python27\Lib\site-
packages\pygraphics` there really was `media.py` ! But why `import media`
didn't work ? (ps: I also tried this `C:\Python27\Scripts\easy_install nose`
in the DOS box, still not work...) Best Regards :)
Answer: Try:
from pygraphics import media
If you're not familiar with importing modules in Python yet, a brief
[primer](http://docs.python.org/reference/simple_stmts.html#grammar-token-
import_stmt) might be useful.
>>> import sys
>>> print sys.path
If you try the code above, you will see a bunch of directories on your system
path. `C:\Python27\Lib\site-packages\` should be one of these.
To import a file located on your system path, you can use `import filename`
(for filename.py). If the file lies in a subdirectory, e.g.
`dir1/dir2/filename.py`, it can be imported using `import dir1.dir2.filename`.
Note: A directory acts as a 'package' if it contains a file called
`__init__.py`. A file that can be imported is called a 'module'.
|
urllib "module object is not callable"
Question: This is my third python project, and I've received an error message: `'module
object' is not callable`.
I know that this means I'm referencing a variable or function incorrectly. But
trial and error hasn't been able to help me solve this.
import urllib
def get_url(url):
'''get_url accepts a URL string and return the server response code, response headers, and contents of the file'''
req_headers = {
'User-Agent': 'Mozilla/5.0 (Windows; U; Windows NT 5.1; en-US) AppleWebKit/525.13 (KHTML, like Gecko) Chrome/0.A.B.C Safari/525.13',
'Referer': 'http://python.org'}
#errors here on next line
request = urllib.request(url, headers=req_headers) # create a request object for the URL
opener = urllib.build_opener() # create an opener object
response = opener.open(request) # open a connection and receive the http response headers + contents
code = response.code
headers = response.headers # headers object
contents = response.read() # contents of the URL (HTML, javascript, css, img, etc.)
return code , headers, contents
testURL = get_url('http://www.urlhere.filename.zip')
print ("outputs: %s" % (testURL,))
I've been using this link for reference:
<http://docs.python.org/release/3.0.1/library/urllib.request.html>
**Traceback:**
Traceback (most recent call last):
File "C:\Project\LinkCrawl\LinkCrawl.py", line 31, in <module>
testURL = get_url('http://www.urlhere.filename.zip')
File "C:\Project\LinkCrawl\LinkCrawl.py", line 21, in get_url
request = urllib.request(url, headers=req_headers) # create a request object for the URL
TypeError: 'module' object is not callable
Answer: In python 3, the `urllib.request` object is a module. You need to call objects
_contained_ in this module. This is an important change from Python 2, if you
are using example code you need to take that into account.
For example, creating the `Request` object and the opener:
request = urllib.request.Request(url, headers=req_headers)
opener = urllib.request.build_opener()
response = opener.open(request)
Read the
[documentation](http://docs.python.org/py3k/library/urllib.request.html)
carefully.
|
Unable to use raw_input() during event handeling in Matplotlib while running pylab -- RuntimeError: can't re-enter readline
Question: I'm trying to write a script that allows the user to manipulate a graph via
event handling in matplotlib, but I need to have them enter some additional
information through the terminal
Calling `raw_input()` seems to break the scripts, and throws a `RuntimeError:
can't re-enter readline` error
here's a simple piece of code to demonstrate this:
import matplotlib.pyplot as plt
import numpy as np
fig = plt.figure()
ax = fig.add_subplot(111)
ax.plot(np.random.rand(10))
def keypress(event):
print 'You press the "%s" key' %event.key
print 'is this true? Type yes or no'
y_or_n = raw_input()
cid = fig.canvas.mpl_connect('key_press_event', keypress)
plt.show()
This works fine if I run it using python, but breaks using ipython --pylab.
Unfortunately, I need the interactive mode
I see other people have had this problem but I haven't seen a solution
Answer: You're running into trouble because matplotlib is still listening for
keypresses. Unfortunately, simply disconnecting its event listening did not
work for me interactively. This solution, however, did work. Though it limits
you in not being able to use the 'y', 'e', 's', 'n', or 'o' keys. There are
workarounds for this if that is a necessity.
import matplotlib.pyplot as plt
import numpy as np
#disable matplotlib keymaps
keyMaps = [key for key in plt.rcParams.keys() if 'keymap.' in key]
for keyMap in keyMaps:
plt.rcParams[keyMap] = ''
str = ''
fig = plt.figure()
ax = fig.add_subplot(111)
ax.plot(np.random.rand(10))
def keypress(event):
global str
if event.key in ['y','e','s','n','o']:
str += event.key
else:
print 'You press the "%s" key' %event.key
print 'is this true? Type yes or no'
if str == 'yes':
print str
str = ''
elif str == 'no':
print str
str = ''
cid = fig.canvas.mpl_connect('key_press_event', keypress)
plt.show()
|
How to download a text file or some objects from webpage using Python?
Question: I am writing a function that downloads and stores the today's list of pre-
release domains .txt file from <http://www.namejet.com/pages/downloads.aspx>.
I am trying to achieve it using json.
import json
import requests
def hello():
r = requests.get('http://www.namejet.com/pages/downloads.aspx')
#Replace with your website URL
with open("a.txt", "w") as f:
#Replace with your file name
for item in r.json or []:
try:
f.write(item['name']['name'] + "\n")
except KeyError:
pass
hello()
I need to download the file which consist of pre-release domains using python.
How can I do that? Is the above code right way to do it?
Answer: I dont't think mechanize is much use for javascript, use
[selenium](http://pypi.python.org/pypi/selenium). Here's an example:
In [1]: from selenium import webdriver
In [2]: browser=webdriver.Chrome() # Select browser that you want to automate
In [3]: browser.get('http://www.namejet.com/pages/downloads.aspx')
In [4]: element=browser.find_element_by_xpath(
'//a[@id="ctl00_ContentPlaceHolder1_hlPreRelease1"]')
In [5]: element.click()
Now you can find `prerelease_10-08-2012.txt` in your download folder and you
can open it in a usual way.
|
How to download text file from website using Python?
Question: I need to write a function that downloads and stores the today's list of pre-
release domains .txt file from `http://www.namejet.com/pages/downloads.aspx.`
So as today is 8th of October you want to get the file "Monday, October 08,
2012". Tried with requests but didn't work. I'm having trouble because the
file is not stored on a fixed URL but is hidden behind some Javascript.
Answer: This one's a little tricky as you're dealing with ASP.NET's
[postback](http://stackoverflow.com/questions/4251157/what-is-a-postback)
system. If this is for anything other than a personal script, I'd be wary as
you're effectively not only using another site's data, but reverse engineering
their software as well (however, IANAL and have no idea about legalities
around these issues in web systems).
What you're going to want to do is check the POST data (using Firebug, Chrome
developer tools, etc) and look for the `__EVENTTARGET` and `__VIEWSTATE`
attributes of the form object. You'll have to decode the `__VIEWSTATE` to be
readable (check out <http://ignatu.co.uk/ViewStateDecoder.aspx>). From there,
I think you _should_ be able to figure out how to get the data you're looking
for.
From Python, it's as easy as:
from urllib2 import urlopen
from urllib import urlencode
data = urlopen('url', urlencode({
'__VIEWSTATE': 'foo',
'__EVENTTARGET': 'bar',
})).read()
|
MacOSX python error on import
Question: Ive recently installed SimpleCV using the osX-Lion setup instructions in page
<https://github.com/ingenuitas/simplecv>
Then I type python in Terminal and when I try the following I get an error.
import SimpleCV
Fatal Python error: (pygame parachute) Segmentation Fault
Abort trap: 6
However I get no errors when i try to import pygame myself. Any fix for this?
Thanks
Answer: Use and follow this instructions of the
[new](https://github.com/sightmachine/simplecv) repository, the you are
[using](https://github.com/ingenuitas/simplecv) have this Alert messages.
> THE SIMPLECV REPO HAS MOVED (As of 4/17/13)
Says the repository title.
> WARNING: The REPO here is for legacy purposes only
|
The right way to architect a cluster in EC2
Question: I'm working on open-source tool which will have to run on a cluster in EC2,
organized in "one master - several slaves" manner. I need some advice on how
to organize things correctly and in the most simple, yet reliable way.
What I basically need is a code which will run on master instance (which user
runs manually) and do the following:
a) Run N slave instances (N came from user)
b) After each instance is up and running - connect by SSH and start something.
c) Keep track on slave instances being alive (by e.g. simply pinging them)
d) If slave instance fails - make sure it is terminated, run another one and
repeat step b)
e) By signal from user - shutdown slave instances.
All this looks pretty simple and straightforward yet I have some questions:
1) Ready solutions. First I'd taken a look at
[Zookeeper](http://zookeeper.apache.org/), but I was frightened by its
complexity. It seems to be an overkill for such a simple thing that I need.
Another thing I found is [StarCluster](http://star.mit.edu/cluster/), it is
also in Python which is nice (my tool is in Python too), but I'm not sure it
does what I need (keeping track, rerunning instances). My question is: are
there simple tools, libraries, frameworks that I'm not aware of?
2) Another way to go will be to implement things myself. The question here is:
are there any pitfalls in my problem that I'm not aware of? It all looks
simple: several calls to API plus some regular ping, but may be I don't see
something here, so it would be really right to use the already written tool?
3) In case of coding it all by myself the question is: to use CloudWatch or
not. Does it really makes any difference for managing internal computation
clusters or it is only better for helping with high-load sites, etc?.
4) My simple architecture does not have any protection from master node
failure. The user runs it, then connects to it via web interface and runs the
cluster, but if master node fails - everything gets broken. The slaves can
check the existence of master node and terminate themselves in case master
node fails. This adds some protection from getting a headless running money-
consuming cluster, but that doesn't solve the problem of graceful restart. How
to solve this?
5) Are there any other thing to know or important materials to read that I
should be familiar with before starting to code this project?
Thank you in advance!
Answer: You might want to take a look at amazon's autoscaling. Obviously this only
handles EC2 instances but handles a lot of the complexity of starting,
stopping and monitoring instances for you.
With AutoScaling you create one or more groups. You tell amazon how to create
more instances in your group (AMI, userData, type of instance, etc.) and how
many instances you want in your group. Amazon will start up as many instances
as required and replace them should they fail.
You can use the api to change the number of required nodes (you can set it to
0 if you don't need any instances at that time) or you can have it based on
cloudwatch metrics. For example if you used SQS to distribute jobs to your
slaves you could configure autoscaling to increase the group size from 0 to
the desired number when there are jobs available and to return the group size
to 0 once the queue becomes empty.
You can also have multiple groups, for example you might have a group that
corresponds to the master node which always has 1 instance (and ec2 will
replace it should it fail) and a second group for slaves which will have 0
instances when there is no work to be done and N instances when there is work
available.
I've not used the EC2 apis from python myself but I hear that boto does a good
job of handling this for you.
|
How to parse YouTube XML using Python?
Question: I am trying to parse the xml from YouTube that is embedded in the code below.
I am trying to display all of the titles. However, I am running into trouble
when I try to print the 'title' only enter lines appear. Any advice?
#import library to do http requests:
import urllib2
#import easy to use xml parser called minidom:
from xml.dom.minidom import parseString
#all these imports are standard on most modern python implementations
#download the file:
file = urllib2.urlopen('http://gdata.youtube.com/feeds/api/users/buzzfeed/uploads?v=2&max-results=50')
#convert to string:
data = file.read()
#close file because we dont need it anymore:
file.close()
#parse the xml you downloaded
dom = parseString(data)
entry=dom.getElementsByTagName('entry')
for node in entry:
video_title=node.getAttribute('title')
print video_title
Answer: Title is not an attribute, it is a child element of an entry.
here is an example how to extract it:
for node in entry:
video_title = node.getElementsByTagName('title')[0].firstChild.nodeValue
print video_title
|
Execute code on App Engine application initialization
Question: When running a Python Web Application on App Engine, we need to set up some
mechanism to execute some code before (or during) the application's
initialization. This means that, in the optimal solution, the code that we
need to run is executed as early as possible. The purpose of this is to allow
for the App Engine remote_api to be initialized before the **local** datastore
is accessed, so as to prevent datastore access conflicts.
This is a very rough example of what we're looking for:
imports (including remote_api)
def some_initialization_function_or_similar (args):
some_init_function_calls(...)
setup_remote_api(...)
access_datastore_the_first_time(...)
Please take this question as reference to the scenario we're looking at:
[Using GAE remote api for debugging from localhost - Connecting too
late?](http://stackoverflow.com/questions/12588327/using-gae-remote-api-for-
debugging-from-localhost-connecting-too-late)
Answer: Assuming you have a single entry point (== script named in app.yaml) you can
just call the desired code after your imports but before you call your main()
function. This means it will be run only when the main script is being
imported, which is only on the first request (hitting that entry point).
If you have multiple entry points, try putting it in appengine_config.py. That
gets loaded pretty early.
|
python: how to store data in mongo via http put
Question: I am trying to create a REST API application using python bottle framework
I'd like to be able to insert data in mongodb via HTTP PUT request.
So far I am able to get response from the mongodb using HTTP GET.
Please help me INSERT data in mongodb via HTTP PUT.
JSON format I have to insert as follows:
{"_id": "id_1", "key_1": "value_1"}
[i am using [this
extension](https://chrome.google.com/webstore/detail/advanced-rest-client-
appl/hgmloofddffdnphfgcellkdfbfbjeloo) to get and put http response]
import json
import bottle
from bottle import route, run, request, abort
from pymongo import Connection
connection = Connection('localhost', 27017)
db = connection.mydatabase
@route('/documents', method='PUT')
def put_document():
data = request.body.readline()
if not data:
abort(400, 'No data received')
entity = json.loads(data)
if not entity.has_key('_id'):
abort(400, 'No _id specified')
try:
db['documents'].save(entity)
except ValidationError as ve:
abort(400, str(ve))
@route('/documents/:id', method='GET')
def get_document(id):
entity = db['documents'].find_one({'_id':id})
if not entity:
abort(404, 'No document with id %s' % id)
return entity
run(host='localhost', port=8080)
Answer: The following revised version of your code seems to work as you intended:
import json
from bottle import route, run, request, abort
from pymongo import Connection
connection = Connection('localhost', 27017)
db = connection.mydatabase
@route('/documents', method='PUT')
def put_document():
data = request.body.readline()
print(data)
if not data:
abort(400, 'No data received')
entity = json.loads(data)
if not entity.has_key('_id'):
abort(400, 'No _id specified')
try:
db.documents.insert(entity)
except ValidationError as ve:
abort(400, str(ve))
@route('/documents/<_id>', method='GET')
def get_document(_id):
entity = db.documents.find_one({'_id': _id})
if not entity:
abort(404, 'No document with id %s' % _id)
return entity
run(host='localhost', port=8080)
I have _MongoDB_ running and executing the script, start the server on
`localhost` port `8080`, I then execute the following commands on a shell with
the expected results:
$ echo '{"_id": "id_1", "key_1": "value_1", "key_2": "value_2"}' | curl -X PUT -d @- http://localhost:8080/documents
$ curl http://localhost:8080/documents/id_1
{"_id": "id_1", "key_1": "value_1", "key_2": "value_2"}
|
How to run a DOS batch file in background using Python?
Question: How to run a DOS batch file in background using Python?
I have a test.bat file in say C:\
Now, I want to run this bat file using python in the background and then I
want to return to the python command line.
I run the batch file using `subprocess.call('path\to\test.bat')` from the
python command line. It runs the batch file in the same window as the python
command line.
If still not clear/ TL.DR-
What is happening:
>>>subprocess.call('C:\test.bat')
(Running test.bat. Can't use python in the same window)
What I want:
>>>subprocess.call('C:\test.bat')
(New commandline window created in the background where test.bat runs in parallel.)
>>>
Answer: This seems to work for me:
import subprocess
p = subprocess.Popen(r'start cmd /c C:\test.bat', shell=True)
p.wait()
print 'done'
|
handling exceptions in settrace 'return' calls
Question: In Python 2.x, the frame object passed into a
[`settrace`](http://docs.python.org/py3k/library/sys.html#sys.settrace)
handler had an `f_exc_type` attribute.
In Python 3.x, this `f_exc_type` has been removed.
If a function is propagating an exception, the trace 'return' is called but
the argument is `None` and `sys.exc_info()` is `(None,None,None)`. This is
described in the
[docs](http://docs.python.org/py3k/library/sys.html#sys.settrace):
> `[return]`A function (or other code block) is about to return. The local
> trace function is called; arg is the value that will be returned, or None if
> the event is caused by an exception being raised. The trace function’s
> return value is ignored.
In Python 3, how can a tracer determine in a `return` hook that an exception
is being propagated? How can it differentiate it from a function returning
`None` normally?
Answer: This does seem fairly broken. It's a bit of a hack, but you can tell the
difference by looking at the bytecode for the last instruction:
import opcode
def tracer(frame, event, arg):
if event == 'return':
if arg is not None or (opcode.opname[frame.f_code.co_code[frame.f_lasti]]]
in ('RETURN_VALUE', 'YIELD_VALUE')):
print('exit via return', arg)
else:
print('exit via exception')
|
re-implement __eq__ to compare sets with symmetric_difference in python
Question: I have a set of filenames coming from two different directories.
currList=set(['pathA/file1', 'pathA/file2', 'pathB/file3', etc.])
My code is processing the files, and need to change currList by comparing it
to its content at the former iteration, say processLst. For that, I compute a
symmetric difference:
toProcess=set(currList).symmetric_difference(set(processList))
Actually, I need the symmetric_difference to operate on the basename
(file1...) not on the complete filename (pathA/file1).
I guess I need to reimplement the `__eq__` operator, but I have no clue how to
do that in python.
1. is reimplementing `__eq__` the right approach? or
2. is there another better/equivalent approach?
Answer: Here is a token (and likely poorly constructed) `itertools` version that
should run a little bit faster if speed ever becomes a concern (although agree
that @Zarkonnen's one-liner is pretty sweet, so +1 there :) ).
from itertools import ifilter
currList = set(['pathA/file1', 'pathA/file2', 'pathB/file3'])
processList=set(['pathA/file1', 'pathA/file9', 'pathA/file3'])
# This can also be a lambda inside the map functions - the speed stays the same
def FileName(f):
return f.split('/')[-1]
# diff will be a set of filenames with no path that will be checked during
# the ifilter process
curr = map(FileName, list(currList))
process = map(FileName, list(processList))
diff = set(curr).symmetric_difference(set(process))
# This filters out any elements from the symmetric difference of the two sets
# where the filename is not in the diff set
results = set(ifilter(lambda x: x.split('/')[-1] in diff,
currList.symmetric_difference(processList)))
|
Error while installing MySQLdb for Python on Mac OSX 10.6.8 with mysql inside XAMPP
Question: I am trying to import MySQldb in python and call the python script from a php
script in XAMPP. Here is what I did:
Environment: 1\. Mac OSX 10.6.8 2\. Python version 2.6 (default)[64bit]
Done so far: 1\. Installed XAMPP 2\. MySQL config path:
/Applications/XAMPP/xamppfiles/bin/mysql_config 3\. Downloaded MySQL-
python-1.2.4b4 4\. edited the site.cfg with config path for MySQL 5\. Ran
following commands
sudo python setup.py clean python setup.py build
Got the following error:
running build
running build_py
copying MySQLdb/release.py -> build/lib.macosx-10.6-universal-2.6/MySQLdb
running build_ext
building '_mysql' extension
gcc-4.2 -fno-strict-aliasing -fno-common -dynamic -DNDEBUG -g -fwrapv -Os -Wall - Wstrict-prototypes -DENABLE_DTRACE -pipe -Dversion_info=(1,2,4,'beta',4) - D__version__=1.2.4b4 -I/Applications/XAMPP/xamppfiles/include/mysql - I/System/Library/Frameworks/Python.framework/Versions/2.6/include/python2.6 -c _mysql.c -o build/temp.macosx-10.6-universal-2.6/_mysql.o -mmacosx-version-min=10.4 -arch i386 -arch ppc -D_P1003_1B_VISIBLE -DSIGNAL_WITH_VIO_CLOSE -DSIGNALS_DONT_BREAK_READ - DIGNORE_SIGHUP_SIGQUIT -DDONT_DECLARE_CXA_PURE_VIRTUAL
In file included from _mysql.c:44:
/Applications/XAMPP/xamppfiles/include/mysql/my_config.h:1053:1: warning: "HAVE_WCSCOLL" redefined
In file included from /System/Library/Frameworks/Python.framework/Versions/2.6/include/python2.6/Python.h:8,
from _mysql.c:29:
/System/Library/Frameworks/Python.framework/Versions/2.6/include/python2.6/pyconfig.h:803:1
: warning: this is the location of the previous definition
/usr/libexec/gcc/powerpc-apple-darwin10/4.2.1/as: assembler
(/usr/bin/../libexec/gcc/darwin/ppc/as or
/usr/bin/../local/libexec/gcc/darwin/ppc/as) for architecture ppc not
installed Installed assemblers are: /usr/bin/../libexec/gcc/darwin/x86_64/as
for architecture x86_64 /usr/bin/../libexec/gcc/darwin/i386/as for
architecture i386 In file included from _mysql.c:44:
/Applications/XAMPP/xamppfiles/include/mysql/my_config.h:1053:1: warning:
"HAVE_WCSCOLL" redefined In file included from
/System/Library/Frameworks/Python.framework/Versions/2.6/include/python2.6/Python.h:8,
from _mysql.c:29:
/System/Library/Frameworks/Python.framework/Versions/2.6/include/python2.6/pyconfig.h:803:1:
warning: this is the location of the previous definition _mysql.c:3131: fatal
error: error writing to -: Broken pipe compilation terminated. lipo: can't
open input file: /var/tmp//ccQsr7Lk.out (No such file or directory) error:
command 'gcc-4.2' failed with exit status 1
Answer: yum install mysql-devel
pip install MySQL-python
|
unable to get values from a login page in web.py
Question: I am using python web.py framework to create a small web application which has
just
1. Login screen (Authentication)
2. Screen with list of records(After succesfull login)
Presently i am trying to create a login screen authentication
I have created an `index.py` file with code as below
**index.py**
import os
import sys
import web
from web import form
from web.contrib.auth import DBAuth
render = web.template.render('templates/')
urls = (
'/', 'Login',
)
app = web.application(urls, globals())
db = web.database(dbn='mysql', db='Python_Web', user='root', pw='redhat')
class Login:
login_form = form.Form(
form.Textbox('username', form.notnull),
form.Password('password', form.notnull),
form.Button('Login'),
)
def GET(self):
form = self.login_form()
return render.login(form)
def POST(self):
# if not self.login_form.validates():
# return render.login(self.login_form)
post = self.login_form()
username = post['username'].value
print username,">>>>>>>>>>>>>>>>>>>>>>username"
password = post['password'].value
ident = db.select('user', where='user_login=$username', vars=locals())
if __name__ == "__main__":
web.internalerror = web.debugerror
app.run()
My **login.html** code
$def with (form)
<!DOCTYPE html PUBLIC "-//W3C//DTD XHTML 1.0 Strict//EN" "http://www.w3.org/TR/xhtml1/DTD/xhtml1-strict.dtd">
<html xmlns="http://www.w3.org/1999/xhtml" lang="en" xml:lang="en">
<head>
<meta http-equiv="Content-Type" content="text/html; charset=UTF-8" />
<title>Log in</title>
</head>
<body>
<div id="container">
<h1>Log in Details</h1>
<form action="" method="post" accept-charset="utf-8">
<p><label for="username">Username:
<input type="text" name="username" id="username" maxlength="254" tabindex="1" />
</label></p>
<p><label for="password">Password:
<input type="password" name="password" id="password" maxlength="254" tabindex="2" />
</label></p>
<p><label for="Login"></label><button id="Login" name="Login">Login</button></p>
</form>
</div>
</body>
When i run the above file with url `www.localhost:9080` in browser i can see
the screen with fields `username, password and login` button , but when i
enter username and password and clicked `login` button and tried to print the
username i cannot fetch any data from the browser and the result showing is as
below
None >>>>>>>>>>>>>>>>>>>>>>username
0.0 (1): SELECT * FROM user WHERE user_login=NULL
Can anyone let me why i am unable fetch the details entered through browser ?,
am i missing anything in the above code and finally all my intention is
to create a `login` page and `validate` the user details by checking in the
database
and `redirect` to the next page if user exits
I request to please help me out in writing the code for fetching the details
from the browser and checking in the database and redirecting to another html
page if user exists. I am really stuck and breaking my heads to complete this
process
Answer: Make sure you validate the form before trying to access any of the inputs
def POST(self):
post = self.login_form()
post.validates()
username = post['username'].value
print username,">>>>>>>>>>>>>>>>>>>>>>username"
password = post['password'].value
ident = db.select('user', where='user_login=$username', vars=locals())
After that change the code works for me. Good luck!
|
Pydev using wrong IPython version?
Question: I have Pydev 2.7, Python 3.2 and IPython 0.13 installed. However, when I run
the interactive console in Eclipse it says
PyDev console: using IPython 0.11
I cannot imagine where IPython 0.11 is supposed to come from. How can I check?
After running the console, `import IPython; IPython.__version__` also gives me
the correct version 0.13.
Is it IPython 0.13 in the console now or is something wrong?
Answer: I think you're fine. I tried
IPython.__version__
and also get 0.13 in the PyDev console:
import sys; print('%s %s' % (sys.executable or sys.platform, sys.version))
C:\Python27\python.exe 2.7.3 (default, Apr 10 2012, 23:31:26) [MSC v.1500 32 bit (Intel)]
PyDev console: using IPython 0.11
import IPython
IPython.__version__
Out[1]: '0.13.1'
|
Unable to switch between two boto.cfg files
Question: I have two _boto.cfg_ files, one for QA and the other for Production. I can
choose dynamically which _boto.cfg_ to choose. When I choose QA and call
`get_all_buckets()` I get all the buckets of QA. But when I change to
Production, it still returns QA buckets. My script is in python.
Is there a way I can disable the boto connection? I have tried to exit from
Python and create a new object but it still returns QA buckets although the
_boto.cfg_ has been updated to Production credentials.
Answer: Are you sure you are picking up different credentials? There is no state
retained across different Python sessions. Try running this little script with
each config file:
>>> import boto
>>> print boto.config.get_value('Credentials', 'aws_access_key_id')
Do you get a different value printed each time? If not, you could try having
two config files, boto1.cfg and boto2.cfg and then setting the environment
variable BOTO_CONFIG to point to one or the other.
|
python, unittest, test a script with command line args
Question: I've written a python script that takes command line arguments and plays one
round of Tic Tac Toe.
running it looks like this...
> run ttt o#xo##x## x 0 1
If the move is legal it then prints the new board layout and whether anyone
won the game
I have to write tests for it using unittest. I dont know how to test the whole
script with various command line parameters, all the examples I've seen seem
to just test individual functions within the script. Also the script uses
`argparse` to parse the parameters
Thanks!
Answer: Refactor your program so that its main action (minus the argparsing) happens
in a "main" function:
def main(args):
...
if __name__ == '__main__':
args = parse_args()
main(args)
Then you can write tests for the behavior of `main` and `parse_args`.
PS. It is possible to use the `subprocess` module to call your program as an
external process and then parse the output, but I think that would be uglier
and unnecessary.
PPS. As an added benefit of writing your program this way, you will be able to
import your program as a module, and call its main function in other scripts.
That might be useful if, for example, you would one day like to build a GUI
for it.
|
What is the difference between Abstract classes and Mixins in Python django
Question: Can anyone please tell what is the difference between Abstract class and Mixin
in Django. I mean if we are to inherit some methods from base class why there
is separate terminology like mixins if that is just a class.
What is diff between baseclass and mixins
Answer: In Python (and Django), **mixin** is a type of multiple inheritance. I tend to
think of them as "specilist" classes that adds a particular functionality to
the class that inheritates it (along with other classes). They aren't really
meant to stand on their own.
Example with Django's `SingleObjectMixin`,
# views.py
from django.http import HttpResponseForbidden, HttpResponseRedirect
from django.core.urlresolvers import reverse
from django.views.generic import View
from django.views.generic.detail import SingleObjectMixin
from books.models import Author
class RecordInterest(View, SingleObjectMixin):
"""Records the current user's interest in an author."""
model = Author
def post(self, request, *args, **kwargs):
if not request.user.is_authenticated():
return HttpResponseForbidden()
# Look up the author we're interested in.
self.object = self.get_object()
# Actually record interest somehow here!
return HttpResponseRedirect(reverse('author-detail', kwargs={'pk': self.object.pk}))
The added
[`SingleObjectMixin`](https://docs.djangoproject.com/en/dev/ref/class-based-
views/mixins-single-object/#django.views.generic.detail.SingleObjectMixin)
will enable you to look up the `author` with just
[`self.get_objects()`](https://docs.djangoproject.com/en/dev/ref/class-based-
views/mixins-single-
object/#django.views.generic.detail.SingleObjectMixin.get_object).
* * *
An abstract class in Python looks like this:
class Base(object):
# This is an abstract class
# This is the method child classes need to implement
def implement_me(self):
raise NotImplementedError("told you so!")
In languages like Java, there is an `Interface` contract which is an
_interface_. However, Python doesn't have such and the _closest_ thing you can
get is an abstract class (you can also read on
[abc](http://docs.python.org/library/abc.html). This is mainly because Python
utlizes [duck typing](http://en.wikipedia.org/wiki/Duck_typing#In_Python)
which kind of removes the need for interfaces. Abstract class enables
polymorphism just like interfaces do.
|
concept of session and cookie in web development python
Question: I am very new to web development, i am working on `web.py` framework to
develop a small web application. suppose the login screen is
`localhost:9090/login`, after the succesfull login it is redirecting to next
page `localhost:9090/details` and after clicking another button `add` its
again redirecting to `localhost:9090/details/details_entry`.
But when i tried directly `localhost:9090/details`on browser its working and
able to see the page without even logged in . So after googling a lot came to
know that i need to use `session concept` , but i am tired as of now for busy
schedule on searching about web concepts in google. Can anyone let me know the
concept of
1. `session` (Actually why it is created and how to use it after login through page in python)
2. Actually whats the complete concept of `user authentication` , What are the steps to follow to create a user login page And steps to follow after user logged in with details what happens when user logouts and how to session code in python
I expect what ever the language it is but the concept of developing login
screen and redirecting to next url by creating some sessions ids is same, so
the user authentication concept is very important and may be this question is
useful to others.
**Edited Code**
**\--------------**
**Login.py**
import os
import sys
import web
from web import form
render = web.template.render('templates/')
urls = (
'/', 'Login',
'/projects', 'Projects',
'/project_details', 'Project_Details',
)
app = web.application(urls, globals())
web.config.debug = False
db = web.database(dbn='mysql', db='Python_Web', user='root', pw='redhat')
settings = {}
store = web.session.DBStore(db, 'sessions')
session = web.session.Session(app, store, initializer={'user': None})
class Login:
login_form = form.Form(
form.Textbox('username', form.notnull),
form.Password('password', form.notnull),
form.Button('Login'),
)
def GET(self):
form = self.login_form()
return render.login(form)
def POST(self):
if not self.login_form.validates():
return render.login(self.login_form)
i = web.input()
username = i.username
password = i.password
user = db.select('user',
where = 'user_login = $username',
vars = {'username': username}
if username == user['username'] and password == user['password']:
session.user = username
raise web.seeother('/projects')
else:
return render.login_error(form)
def auth_required(func):
def proxyfunc(self, *args, **kw):
print session.user,"=======> Session stored"
try:
if session.user:
return func(self, *args, **kw)
except:
pass
raise web.seeother("/")
return proxyfunc
class Projects:
project_list = form.Form(
form.Button('Add Project'),
)
@auth_required
def GET(self):
project_form = self.project_list()
return render.projects(project_form)
def POST(self):
raise web.seeother('/project_details')
if __name__ == "__main__":
web.internalerror = web.debugerror
app.run()
In the above code after successfull login the page is redirecting to next
page. Here i need to implement session concept, but i was stuck on where to
implement session code in the above code. Can anyone please point me to a
right way on where to write session code in the above py code for login page.
After this worked need to implement logout functionality in the same py file
Edited code after implementing `auth_required` function and got the below
error
**Result:**
Traceback (most recent call last):
File "/usr/lib/python2.7/site-packages/web/application.py", line 239, in process
return self.handle()
File "/usr/lib/python2.7/site-packages/web/application.py", line 230, in handle
return self._delegate(fn, self.fvars, args)
File "/usr/lib/python2.7/site-packages/web/application.py", line 420, in _delegate
return handle_class(cls)
File "/usr/lib/python2.7/site-packages/web/application.py", line 396, in handle_class
return tocall(*args)
File "/home/local/user/python_webcode/index.py", line 102, in proxyfunc
print session.user,"=======> Session Stored"
File "/usr/lib/python2.7/site-packages/web/session.py", line 71, in __getattr__
return getattr(self._data, name)
AttributeError: 'ThreadedDict' object has no attribute 'user'
Answer: web.py provides [session](http://webpy.org/cookbook/sessions) abstraction and
several session stores. What you have to do, is to write login controller,
display the form on GET, and find user and perform password check on POST,
then store the user in session and kill the session on logout. After it you
may write decorator that checks if user exists in session to use it over
controller methods. Anyway, user authentication concept is mostly the same in
all web apps.
If you need already working solution for web.py then you may take a look at
this module: <http://jpscaletti.com/webpy_auth/>
If you decided to implement login youself, the simplest auth decorator will
probably look like this:
def auth_required(func):
def proxyfunc(self, *args, **kw):
try:
if session.user:
# user is logged in
return func(self, *args, **kw)
except:
pass
# user is not logged in
raise web.seeother("/login")
return proxyfunc
Then you will be able to use @auth_required before your GET and POST methods
in controllers like this:
class Projects:
@auth_required
def GET(self):
pass
|
The __str__ method returning a unicode string works in one environment but fails in another
Question: I thought, I understood unicode and python. But this issue confuses me a lot.
Look at this small test program:
# -*- coding: utf-8 -*-
class TestC(object):
def __str__(self):
return u'äöü'
import sys
print sys.version
print sys.stdin.encoding
print sys.stdout.encoding
print u'öäü' #this works
x = TestC()
print x #this doesn't always work
When I run this from my bash terminal on ubuntu, I get the following result:
2.7.3 (default, Aug 1 2012, 05:14:39)
[GCC 4.6.3]
utf-8
utf-8
öäü
Traceback (most recent call last):
File "test_mod.py", line 14, in <module>
print x #this doesn't '
UnicodeEncodeError: 'ascii' codec can't encode characters in position 0-2: ordinal not in range(128)
However, when I run the same thing from within eclipse (using the pydev
module), both print statements work flawlessly. The console windows says:
2.7.3 (default, Aug 1 2012, 05:14:39)
[GCC 4.6.3]
utf-8
utf-8
öäü
äöü
Can someone please explain to me what the issue is? Why does the __str__
method work in one case but not in the other? What is the best way to fix
this?
Answer: See this related question: [Python __str__ versus
__unicode__](http://stackoverflow.com/questions/1307014/python-str-versus-
unicode)
Basically, you should probably be implementing the special method
`__unicode__` rather than `__str__`, and add a stub `__str__` that calls
`__unicode__`:
def __str__(self):
return unicode(self).encode('utf-8')
|
permission denied when creating an .html file in python
Question: so this is my first python experience. I have a list of images in folder that
I'm trying to convert to html pages. For that I have the following code:
import inspect, os, errno, markup
path = os.path.dirname(os.path.abspath(inspect.getfile(inspect.currentframe())))+'/www/img/'
print path
for f in os.listdir(path):
counter = 1
page = markup.page()
page.init(charset="UTF-8")
from markup import oneliner as e
page.a(e.img(src='img/'+f, width=1024, height=768), href='')
final = open('/index'+str(counter)+'.html','w')
final.write(page)
and I get an `IOError: [Errno 13] Permission denied: '/index1.html'`
message.... any clues or ideas are much appreciated. thanks!
Answer: I think the main problem is related to file permissions of root folder (`/`).
Try running the script as root or pick some other directory that you are sure
you have write access to.
|
How to send Python variable to bash variable?
Question: I am trying to use Python to select a variable from a list, then speak it
outloud using the bash command. Right now I have something like this
foo = ["a","b","c","d"]
from random import choice
x = choice(foo)
foo.remove(x)
from os import system
system('say x')
This says "x", what I need is for it to say the value of the `x` variable.
Answer: I suppose you can use `os.system`, but better might be `subprocess`:
import subprocess
subprocess.call(['say',x])
|
How to get all YouTube comments with Python's gdata module?
Question: Looking to grab all the comments from a given video, rather than go one page
at a time.
from gdata import youtube as yt
from gdata.youtube import service as yts
client = yts.YouTubeService()
client.ClientLogin(username, pwd) #the pwd might need to be application specific fyi
comments = client.GetYouTubeVideoComments(video_id='the_id')
a_comment = comments.entry[0]
The above code with let you grab a single comment, likely the most recent
comment, but I'm looking for a way to grab _all_ the comments at once. Is this
possible with Python's `gdata` module?
* * *
The Youtube API docs for
[comments](https://developers.google.com/youtube/2.0/developers_guide_protocol_comments),
the comment feed [docs](http://gdata-python-
client.googlecode.com/hg/pydocs/gdata.youtube.html#YouTubeVideoCommentFeed)
and the Python API
[docs](https://developers.google.com/youtube/1.0/developers_guide_python#Comments)
Answer: The following achieves what you asked for using the [Python YouTube
API](https://gdata-python-client.googlecode.com/hg/pydocs/gdata.youtube.html):
from gdata.youtube import service
USERNAME = '[email protected]'
PASSWORD = 'a_very_long_password'
VIDEO_ID = 'wf_IIbT8HGk'
def comments_generator(client, video_id):
comment_feed = client.GetYouTubeVideoCommentFeed(video_id=video_id)
while comment_feed is not None:
for comment in comment_feed.entry:
yield comment
next_link = comment_feed.GetNextLink()
if next_link is None:
comment_feed = None
else:
comment_feed = client.GetYouTubeVideoCommentFeed(next_link.href)
client = service.YouTubeService()
client.ClientLogin(USERNAME, PASSWORD)
for comment in comments_generator(client, VIDEO_ID):
author_name = comment.author[0].name.text
text = comment.content.text
print("{}: {}".format(author_name, text))
Unfortunately the API limits the number of entries that can be retrieved to
**1000**. This was the error I got when I tried a tweaked version with a hand
crafted `GetYouTubeVideoCommentFeed` URL parameter:
gdata.service.RequestError: {'status': 400, 'body': 'You cannot request beyond item 1000.', 'reason': 'Bad Request'}
Note that the same principle should apply to retrieve entries in other feeds
of the API.
If you want to hand craft the `GetYouTubeVideoCommentFeed` URL parameter, its
format is:
'https://gdata.youtube.com/feeds/api/videos/{video_id}/comments?start-index={start_index}&max-results={max_results}'
The following restrictions apply: `start-index <= 1000` and `max-results <=
50`.
|
Subversion Get Text Status Data in Python Commit Hooks
Question: I'm looking for a way to extend Python Commit Hooks such that I can ONLY find
out all the files that were modified excluding all the revision properties
changed.
Is there a SVN.Core or SVN.fs or another SVN import lib function that I could
use?
I'm currently looking into svn_fs_txn_prop
but haven't had much luck.
Thanks in Advance.
Answer: Using Subversion Core library in Python you can create a class to read through
different Subversion Properties associated with a commit.
you can call something like:
changeCollector = svn.repos.ChangeCollector(self.fs_obj,self.fsroot,self.pool);
for path, change in changeCollector.changes.items():
# this is the property that i want
change.text_changed
|
python listing and counting values
Question: In the sample data given below (stored in a file), I need to find distinct
'ids' in each 'item' category in the fastest way possible. I can do this by
going through each line and then finding all item sets and then count, but I
am looking for a faster method such as 'Counter' or 'itemgetter'.
"infile.txt"
id item
444 Anemia
444 liver
444 Anemia
444 Anemia
222 liver
222 pancreas
222 liver
222 Anemia
444 pancreas
444 pancreas
444 Anemia
001 Iiver
001 pancreas
111 pancreas
111 liver
111 liver
111 pancreas
555 pancreas
555 liver
555 pancreas
555 liver
555 pancreas
555 liver
I need the output something like the following
item count ids
pancreas 5 001, 111, 222, 444, 555
liver 5 111,222,444,555,001
Anemia 2 222,444
Answer: I'd use a defaultdict with a `set`
from collections import defaultdict
d = defaultdict(set)
with open(datafile) as f:
for line in f:
my_id,item = line.split()
d[item].add(my_id)
for item in d:
print item,len(d[item]),sorted(d[item])
|
Python web scraping pauses
Question: I have the following code:
#!/usr/bin/env python
from mechanize import Browser
from BeautifulSoup import BeautifulSoup
mech = Browser()
mech.set_handle_robots(False)
url = "http://storage.googleapis.com/patents/retro/2011/ad20111231-02.zip"
page = mech.open(url)
html = page.read()
soup = BeautifulSoup(html)
print soup.prettify()
really simple web scraper trying to download a .zip file from a web page. When
I run this code, and bearing in mind this file is 4kb, the program just does
not finish, as if it is in an infinite while loop. what I have done here?
Answer: Try putting `print html` after you do your `page.read()`. You may not be
getting what you think you are, it sounds like you're receiving an error page
rather than the file itself. I'm not sure if you're even handling the file
correctly, you might find a better approach here: [Download all the
links(related documents) on a webpage using
Python](http://stackoverflow.com/questions/5974595/download-all-the-
linksrelated-documents-on-a-webpage-using-python).
The zip file isn't 4KB, btw, it's ~87MB and contains a _784MB_ XML file, which
you should be able to confirm by hitting that URL in a browser and downloading
it. It may not be an infinite loop that's the problem, it's just taking a long
time to load.
You're also trying to pass the data in as HTML when it's zip-archived XML. If
(once you actually _have_ the file) you store the response data in a
`StringIO`, you'll be able to unzip it in memory ([as outlined
here](http://stackoverflow.com/questions/10908877/extracting-a-zipfile-to-
memory)). You will then need to [explicitly tell
`BeautifulSoup`](http://www.crummy.com/software/BeautifulSoup/bs4/doc/#id11)
that you're passing it XML.
soup = BeautifulSoup(html, 'xml')
This will require you to [install
lxml](http://www.crummy.com/software/BeautifulSoup/bs4/doc/#parser-
installation), but that will work out to your advantage, as it's possibly the
fastest XML parser under Python.
One last thing:
mech.set_handle_robots(False)
url = "http://storage.googleapis.com/patents/retro/2011/ad20111231-02.zip"
I was under the impression Google set up their `robots.txt` to disallow
scraping as much as possible. If you're still unable to even download a copy
of the file, I'd recommend trying `Selenium`; it's a lot like `mechanize` but
controls actual browsers, like Chrome & Firefox, so it will be a legitimate
browser request.
|
cannot run python script file using windows prompt
Question: I am trying to run a python script from the windows command prompt, but I
receive the following error message:
_"python: can't open file 'pacman.py': [Errno 2] No such file or directory"_
when I try the command:
c:\Program Files (x86)\Python27>python pacman.py
This particular python script file _pacman.py_ is located in the following
folder:
C:\Users\Chris\Dropbox\edX\CS188x\search
So I added this folder to PYTHONPATH and confirmed that is was there using the
following code:
>>> import sys
>>> sys.path
['', 'C:\\Program Files (x86)\\Python27\\Lib\\idlelib', 'C:\\Users\\Chris\\Dropbox\\edX\\CS188x\\search', 'C:\\windows\\syste...
I also checked the permissions on this file:
>>> os.access("C:\Users\Chris\Dropbox\edX\CS188x\search\pacman.py",os.W_OK)
True
>>> os.access("C:\Users\Chris\Dropbox\edX\CS188x\search\pacman.py",os.R_OK)
True
>>> os.access("C:\Users\Chris\Dropbox\edX\CS188x\search\pacman.py",os.X_OK)
True
So I am really not sure why I can't run this file, even though its path has
been added to PYTHONPATH. Any help would be greatly appreciated. Thank you.
Answer: PYTHONPATH is used by the python interpreter. It is not the same as Windows'
PATH environment variable. You can't use it as a search path for passing files
to the interpreter on the command line.
So, you need to specify a valid path to the file. Either by using he same
command as you've been trying with the difference being your current directory
is the same as the location of pacman.py, or by specifying the full path to
the file.
|
How python handles object instantiation in a ' for' loop
Question: I've got a highly complex class :
class C:
pass
And I've got this test code :
for j in range(10):
c = C()
print c
Which gives :
<__main__.C instance at 0x7f7336a6cb00>
<__main__.C instance at 0x7f7336a6cab8>
<__main__.C instance at 0x7f7336a6cb00>
<__main__.C instance at 0x7f7336a6cab8>
<__main__.C instance at 0x7f7336a6cb00>
<__main__.C instance at 0x7f7336a6cab8>
<__main__.C instance at 0x7f7336a6cb00>
<__main__.C instance at 0x7f7336a6cab8>
<__main__.C instance at 0x7f7336a6cb00>
<__main__.C instance at 0x7f7336a6cab8>
One can easily see that Python switches on two different values. In some
cases, this can be catastrophic (for example if we store the objects in some
other complex object).
Now, if I store the objects in a List :
lst = []
for j in range(10):
c = C()
lst.append(c)
print c
I get this :
<__main__.C instance at 0x7fd8f8f7eb00>
<__main__.C instance at 0x7fd8f8f7eab8>
<__main__.C instance at 0x7fd8f8f7eb48>
<__main__.C instance at 0x7fd8f8f7eb90>
<__main__.C instance at 0x7fd8f8f7ebd8>
<__main__.C instance at 0x7fd8f8f7ec20>
<__main__.C instance at 0x7fd8f8f7ec68>
<__main__.C instance at 0x7fd8f8f7ecb0>
<__main__.C instance at 0x7fd8f8f7ecf8>
<__main__.C instance at 0x7fd8f8f7ed40>
Which solves the case.
So now, I have to ask a question... Does anyone could explain with complex
words (I mean, deeply) how Python behave with the objects references ? I
suppose, it is a matter of optimization (to spare memory, or prevent leaks,
...)
Thank a lot.
**EDIT :** Ok so, let's be more specific. I'm quite aware that python has to
collect garbage sometimes... But, in my case :
I had a list returned by a Cython defined class : class 'Network' that manages
a 'Node's list (both Network and Node class are defined in a `Cython
extension`). Each Node has a an object [then casted into (void *)] 'userdata'
object. The Nodes list is populated from inside cython, while the UserData are
populated inside the Python script. So in python, I had the following :
...
def some_python_class_method(self):
nodes = self.netBinding.GetNetwork().get_nodes()
...
for item in it:
a_site = PyLabSiteEvent()
#l_site.append(a_site) # WARN : Required to get an instance on 'a_site'
# that persits - workaround...
item.SetUserData(a_site)
Reusing this node list later on in the same python class using the same cython
getter :
def some_other_python_class_method(self, node):
s_data = node.GetUserData()
...
So, it seems that with the storage made in the node list's UserDatas, my
python script was completely blind and was freeing/reusing memory. It worked
by referencing a second time (but apparently a first one for python side),
using an additional list (here : 'l_site'). This is why I had to know a bit
more about Python itself, but it seems that the way I implemented the
communication between Python and `Cython` is responsible for the issues a had
to face.
Answer: There is no need to be "complex" here: In the first example, you keep no other
reference to the object referenced by the name "c" - when running the code in
the line "c = C()" on subsequent iterations of the loop, the one reference
previously held in "c" is lost.
Since standard Python uses reference counting to keep track of when it should
delete objects from memory, as at this moment the reference counting for the
object of the previous loop interation reaches 0, it is destroyed, and its
memory is made available for other objects.
Why do you have 2 changing values? Because at the moment the object in the new
iteration is created - i.e. when Python executes the expression to the right
side of the `=` in `c = C()`, the object of the precvious iteration still
exists, referenced by the name `c` \- so the new object is constructed at
another memory locaton. Python then proceeds to the assignment of the new
object to `c` at which point the previous object is destroyed as described
above - which means that on the next (3rd) iteration, that memory will be
available for a new instance of `C`.
On the second example, the newly created objects never loose reference, and
therefore their memory is not freed at all - new objects always take up a new
memory location.
**Most important of all:** The purpose of using a high level language such as
Python or others, is _not_ having to worry about memory allocation. The
language takes care of that to you. In this case, the CPython (standard)
implementation does just the right thing, as you noticed. Other
implementations such as Pypy or Jython can have completely different behavior
in regards to the "memory location" of each instances in the above examples,
but all conforming implementatons (including these 3) will behave exactly the
same from the "point of view" of the Python program: (1) It does have access
to the instances it keeps a reference to, (2) the data of these instances is
not corrupted or mangled in anyway.
|
Loading Django apps for development
Question: So, I've got this set-up in which I installed a django project (the directory
containing the settings.py and manage.py) in the site-packages directory of my
python installation. I've done this to use apps from other packages, which
works nicely. I noticed however, that when I'm developing, the development
server (manage.py runserver) loads files from the site-package directory.
Example: There is a file, views.py, that loads models from models.py using:
from models import Project, Test
Because of a small error within the production code I tried to fix, still pops
up within the development server, and the django error page (such a nice
feature) shows the old code from the file that's installed in site-packages.
So, I put in this line:
import models
print models.__file__
and the result of that is exactly the file I want, from my development
directory. The next line, from models import Project, Test loads models from
the site-package directory, which is totally not what I want.
I guess I've polluted the namespace, I'm guessing that the from-import imports
already loaded imports from memory, but that the normal import-line imports a
module that isn't in memory yet. This apparently leads to the strange effect
of being successfully able to change views.py and see the changes in the
development server.
Anybody's got any idea how to fix this?
System info:
* Python2.7
* Django1.3
* Debian
Answer: This is what [virtualenv](http://www.virtualenv.org/en/latest/index.html) is
for. It creates isolated development environments, and is indispensable for
working on multiple projects/versions at once.
|
Django mod_python logging issues
Question: I'm trying to debug my view file in Django. I'm using Django 1.3 with
mod_python on server.
How can I see some out from my view file. I already try to use standart
logging configuration
LOGGING = {
'version': 1,
'disable_existing_loggers': True,
'formatters': {
'standard': {
'format' : "[%(asctime)s] %(levelname)s [%(name)s:%(lineno)s] %(message)s",
'datefmt' : "%d/%b/%Y %H:%M:%S"
},
},
'handlers': {
'null': {
'level':'DEBUG',
'class':'django.utils.log.NullHandler',
},
'logfile': {
'level':'DEBUG',
'class':'logging.handlers.RotatingFileHandler',
'filename': SITE_ROOT + "/logfile",
'maxBytes': 50000,
'backupCount': 2,
'formatter': 'standard',
},
'console':{
'level':'INFO',
'class':'logging.StreamHandler',
'formatter': 'standard'
},
},
'loggers': {
'django': {
'handlers':['console'],
'propagate': True,
'level':'WARN',
},
'django.db.backends': {
'handlers': ['console'],
'level': 'DEBUG',
'propagate': False,
},
'customer_portal': {
'handlers': ['console', 'logfile'],
'level': 'DEBUG',
},
}
}
I'm write in my view file:
import logging
log = logging.getLogger('customer_portal')
log.debug("Some data")
But file with log is not created. Thanks for help.
Answer: I cut/paste your code and it is working for me. Perhaps there are incorrect
permissions on the directory and/or file you are trying to write to?
|
Why does this extremely simple wxPython AUI application crash on launch?
Question: I'm making a Regular Expression testing tool for work. I would like it to be a
simple AUI application, but after transferring what seems to me to be the
**core** of an AUI application from the demo to my code, it crashes on
startup. I can only see the wxPython log window for a fraction of a second
before it disappears, and the code produces no errors in the console.
Here is the troublesome frame. If I comment out all the `_mgr` lines, the
application runs just fine.
class RegexTesterFrame(wx.Frame):
def __init__(self):
wx.Frame.__init__(
self, None, -1, 'Regex tester', (100, 100),
(400, 400), wx.DEFAULT_FRAME_STYLE
)
self.initialize_components()
self.CreateStatusBar()
def initialize_components(self):
self._mgr = wx.aui.AuiManager()
self._mgr.SetManagedWindow(self)
self._perspectives = []
self._mgr.AddPane(
wx.CheckBox(self, -1, 'test'),
wx.aui.AuiPaneInfo().Name('Test pane').Caption('Test caption').Top()
)
self._mgr.Update()
self.Bind(wx.EVT_CLOSE, self.on_close)
def on_close(self, event):
self._mgr.UnInit()
del self._mgr
self.Destroy()
Here is the full code (~100 lines): <http://pastebin.com/xZS2g1fq>
And here is the demo I'm working from (LARGE): <http://pastebin.com/G26BMYZx>
I'm curious about two things - why does the application crash, and why do I
get no error output when wxPython applications crash in general.
Answer: I've struggled with this since yesterday, but as usual, the minute I ask the
question on StackOverflow I figure it out. First of all I got the application
to output error information in a message box instead of stderr:
def main():
try:
app = RegexTesterApp(True)
app.MainLoop()
except:
import traceback
xc = traceback.format_exception(*sys.exc_info())
wx.MessageBox(''.join(xc))
Then the error revealed that `wx.aui` was a module that I hadn't imported.
Importing it fixed the crash.
|
Build an Eclipse workspace with TeamCity
Question: I am in the process of converting our existing custom continuous build system
to use TeamCity. This appears to work well for most of our build scenarios but
one.
We have a hardware project that is set up to build using Eclipse configured
with a specific set of tool chains. Developers run the IDE, and for lack of an
Eclipse build runner, TeamCity builds the project from the commandline runner
using python scripts.
The TeamCity build process is as follows:
* Delete the contents of the Eclipse workspace.
* import all the Eclipse projects into the workspace.
* build the workspace.
The problems with this approach are as follows:
* There is no build runner for Eclipse. The scripts work, but there is overhead in developing and maintaining the scripts. This is the very thing we are trying to get away from.
* There is no TeamCity parsing of the output (gcc and eclipse). I have to redirect the eclipse output to file, and when the Eclipse process finishes, parse the file for errors, warnings, progress status, etc., in order to inject the appropriate TeamCity service message to stdout. Again this kind of overhead is the very thing we are trying to get away from.
Given no Eclipse build runner just days away from release, is there a better
mechanism for loading and building an Eclipse workspace with TeamCity?
Given the commandline runner script solution, is there a better machnism for
capturing and displaying errors, warnings, etc.?
Answer: This may not be the best approach for you at this particular time in your
release cycle, given that you are so close to your release deadline, but I
would use Maven for the build and use the M2E plugin to provide Maven
integration inside of Eclipse.
While using Maven as a build tool is usually not overly complex, it is
sometimes not trivial to convert an existing project to use it.
I would suggest that you start off your next release cycle by enabling Maven
as your build tool - TeamCity fully supports the Maven build runner.
|
Python telnetlib read's only print "bs"
Question: I'm trying to do some telnet automation with Python (only _pure_ Python). When
I try to print some of my read's in the function `read_until`, all I see are a
series of `bs`'s -- that's `bs`, as in the `backspace` character, not
something else. :-)
Does anyone know if there's some kind of setting I can change in the on `tn`,
my instance of the `Telnet` class, or correct this? Or is this something that
my host is spewing back? I've done some Googling on the `telnetlib` library,
and I haven't seen many examples where folks have output from the
`Telnet.read_until` function.
This is a cut-down version of my code:
import getpass
import sys
import telnetlib
HOST = "blahblah"
def writeline(data):
local.write(data + '\n')
def read_until(tn, cue, timeout=2):
print 'Before read until "%s"' % cue
print tn.read_until(cue, timeout)
print 'After read until "%s"' % cue
def tn_write(tn, text, msg=''):
if not msg:
msg = text
print 'Before writing "%s"' % msg
tn.write(text)
print 'After writing "%s"' % msg
user = 'me'
password = getpass.getpass()
tn = telnetlib.Telnet(HOST)
read_until(tn, "Username: ")
tn_write(tn, user + "\n", user)
if password:
read_until(tn, "Password: ")
tn_write(tn, password + "\n", 'password')
read_until(tn, "continue")
tn_write(tn, "\n", '<Enter>')
#tn.write("vt100\n")
tn_write(tn, 'main_menu' + '\n', 'start menu')
read_until(tn, 'Selection: ')
I don't think it matters, but I'm using Python 2.7 on Windows.
Answer: I figured out the problem here. I tried writing my commands with both `\n` and
`\r` but not both combined. When I changed to `'\r\n'`, I got the expected
output.
|
Python read text files in numpy array when empty or single line
Question: I am reading from text files with the code below:
import numpy as np
my_data = np.genfromtxt(resultsDirectory+'/Points.txt', delimiter=' ')
PointX = my_data[:,5]
PointY = my_data[:,11]
My input files are typically like this -
ParamA : 0 ParamB : 7 ParamC : 0 ParamD : 1 Result : FAIL Time : 0 Epsilon : 0.5
ParamA : 0 ParamB : 11 ParamC : 0 ParamD : 1 Result : FAIL Time : 2 Epsilon : 0.5
ParamA : 0 ParamB : 7 ParamC : 0 ParamD : 3 Result : FAIL Time : 2 Epsilon : 0.25
ParamA : 0 ParamB : 13 ParamC : 0 ParamD : 1 Result : FAIL Time : 7 Epsilon : 0.25
ParamA : 0 ParamB : 7 ParamC : 0 ParamD : 4 Result : FAIL Time : 8 Epsilon : 0.125
ParamA : 0 ParamB : 8 ParamC : 0 ParamD : 2 Result : FAIL Time : 1 Epsilon : 0.125
ParamA : 0 ParamB : 8 ParamC : 0 ParamD : 3 Result : FAIL Time : 3 Epsilon : 0.125
ParamA : 0 ParamB : 8 ParamC : 0 ParamD : 4 Result : FAIL Time : 6 Epsilon : 0.125
ParamA : 0 ParamB : 9 ParamC : 0 ParamD : 2 Result : FAIL Time : 6 Epsilon : 0.125
ParamA : 0 ParamB : 10 ParamC : 0 ParamD : 2 Result : FAIL Time : 5 Epsilon : 0.125
ParamA : 0 ParamB : 14 ParamC : 0 ParamD : 1 Result : FAIL Time : 6 Epsilon : 0.125
When I extract PointX from this I get
PointX = [7 11 7 13 7 8 8 8 9 10 14]
PointY = [1 1 3 1 4 2 3 4 2 2 1]
Now, sometimes my text files contain only a single line or are even empty.
For example, if the text file has only one line, the my_data array is like
this -
[ nan nan 0. nan nan 7. nan nan 0. nan nan 1.
nan nan nan nan nan 0. nan nan 0.5]
In this case, `my_data.shape` returns `(21,)`.
However reading the array `PointX` or `PointY` gives me an error as
`IndexError: invalid index`. I wanted `PointX=[7]` and `PointY=[1]`. Or if the
text file is empty, it should be `PointX=[]` and `PointY=[]`.
How exactly should I solve this problem? Also I need my `PointX` and `PointY`
to be an array in order not to break the code which is dependent on it.
Thank you.
Answer: Unfortunately, `genfromtxt` returns a 1D array if given a file with only one
line, and returns a 2D array if given more than one line. You could handle the
discrepancy by reshaping:
import numpy as np
my_data = np.genfromtxt('data', delimiter=' ')
if my_data.ndim == 1:
my_data = my_data.reshape(1, -1)
PointX = my_data[:,5]
PointY = my_data[:,11]
print(PointX)
print(PointY)
yields
[ 7.]
[ 1.]
|
Integer division: is a//b == int(a/b) true for all integers a,b?
Question: I know that integer division will always return the same answer as truncation
of a floating point result if the numbers are both positive. Is it true if one
or both of them are negative?
I was just curious to know if there was an integer division expression that
would return the same results in Python 2 and Python 3 (and yes, I know about
`from __future__ import division`).
P.S. Let's ignore floating point overflow for the moment.
Answer: It is not true in Python 3, and you can test it for yourself:
>>> int(-1/3) == -1//3
False
Integer division and modulo of `a` and `b` giving `q` (quotient) and `r`
(remainder) respectively will always return numbers that satisfy `b*q + r ==
a` and `(a*b)>0 == q>0` (i.e. `a*b` and `q` have the same sign) and `abs(r) <
abs(q)`. The expression `int(q)` simply always rounds towards 0 if `q` is a
floating point number.
It will always be true for Python 2 unless you do `from __future__ import
division`, but that's because `a/b == a//b` if `a` and `b` are integers in
Python 2.
|
Finding the square root using Newton's method (errors!)
Question: I'm working to finish a math problem that approximates the square root of a
number using Newton's guess and check method in Python. The user is supposed
to enter a number, an initial guess for the number, and how many times they
want to check their answer before returning. To make things easier and get to
know Python (I've only just started learning the language a couple of months
ago) I broke it up into a number of smaller functions; the problem now,
though, is that I'm having trouble calling each function and passing the
numbers through.
Here is my code, with comments to help (each function is in order of use):
# This program approximates the square root of a number (entered by the user)
# using Newton's method (guess-and-check). I started with one long function,
# but after research, have attempted to apply smaller functions on top of each
# other.
# * NEED TO: call functions properly; implement a counting loop so the
# goodGuess function can only be accessed the certain # of times the user
# specifies. Even if the - .001 range isn't reached, it should return.
# sqrtNewt is basically the main, which initiates user input.
def sqrtNewt():
# c equals a running count initiated at the beginning of the program, to
# use variable count.
print("This will approximate the square root of a number, using a guess-and-check process.")
x = eval(input("Please type in a positive number to find the square root of: "))
guess = eval(input("Please type in a guess for the square root of the number you entered: "))
count = eval(input("Please enter how many times would you like this program to improve your initial guess: "))
avg = average(guess, x)
g, avg = improveG(guess, x)
final = goodGuess(avg, x)
guess = square_root(guess, x, count)
compare(guess, x)
# Average function is called; is the first step that gives an initial average,
# which implements through smaller layers of simple functions stacked on each
# other.
def average(guess, x) :
return ((guess + x) / 2)
# An improvement function which builds upon the original average function.
def improveG(guess, x) :
return average(guess, x/guess)
# A function which determines if the difference between guess X guess minus the
# original number results in an absolute vale less than 0.001. Not taking
# absolute values (like if guess times guess was greater than x) might result
# in errors
from math import *
def goodGuess(avg, x) :
num = abs(avg * avg - x)
return (num < 0.001)
# A function that, if not satisfied, continues to "tap" other functions for
# better guess outputs. i.e. as long as the guess is not good enough, keep
# improving the guess.
def square_root(guess, x, count) :
while(not goodGuess(avg, x)):
c = 0
c = c + 1
if (c < count):
guess = improveG(guess, x)
elif (c == count):
return guess
else :
pass
# Function is used to check the difference between guess and the sqrt method
# applied to the user input.
import math
def compare(guess, x):
diff = math.sqrt(x) - guess
print("The following is the difference between the approximation")
print("and the Math.sqrt method, not rounded:", diff)
sqrtNewt()
Currently, I get this error: `g, avg = improveG(guess, x) TypeError: 'float'
object is not iterable.` The final function uses the final iteration of the
guess to subtract from the math square root method, and returns the overall
difference. Am I even doing this right? Working code would be appreciated,
with suggestions, if you can provide it. Again, I'm a newbie, so I apologize
for misconceptions or blind obvious errors.
Answer: Implementation of the newton method:
It should be fairly easy to add little tweaks to it when needed. Try, and tell
us when you get stuck.
from math import *
def average(a, b):
return (a + b) / 2.0
def improve(guess, x):
return average(guess, x/guess)
def good_enough(guess, x):
d = abs(guess*guess - x)
return (d < 0.001)
def square_root(guess, x):
while(not good_enough(guess, x)):
guess = improve(guess, x)
return guess
def my_sqrt(x):
r = square_root(1, x)
return r
>>> my_sqrt(16)
4.0000006366929393
NOTE: you will find enough exaples on how to use raw input here at SO or
googling, BUT, if you are counting loops, the `c=0` has to be outside the
loop, or you will be stuck in an infinite loop.
Quiqk and dirty, lots of ways to improve:
from math import *
def average(a, b):
return (a + b) / 2.0
def improve(guess, x):
return average(guess, x/guess)
def square_root(guess, x, c):
guesscount=0
while guesscount < c :
guesscount+=1
guess = improve(guess, x)
return guess
def my_sqrt(x,c):
r = square_root(1, x, c)
return r
number=int(raw_input('Enter a positive number'))
i_guess=int(raw_input('Enter an initial guess'))
times=int(raw_input('How many times would you like this program to improve your initial guess:'))
answer=my_sqrt(number,times)
print 'sqrt is approximately ' + str(answer)
print 'difference between your guess and sqrt is ' + str(abs(i_guess-answer))
|
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