BAAI_bge-large-en-v1.5/recursive_chunks/_chat_templating.txt_chunk_11.txt

This template wraps each message in <|im_start|> and <|im_end|> tokens, and simply writes the role as a string, which
allows for flexibility in the roles you train with. The output looks like this:
text
<|im_start|>system
You are a helpful chatbot that will do its best not to say anything so stupid that people tweet about it.<|im_end|>
<|im_start|>user
How are you?<|im_end|>
<|im_start|>assistant
I'm doing great!<|im_end|>
The "user", "system" and "assistant" roles are the standard for chat, and we recommend using them when it makes sense,
particularly if you want your model to operate well with [TextGenerationPipeline]. However, you are not limited
to these roles - templating is extremely flexible, and any string can be a role.
I want to add some chat templates! How should I get started?
If you have any chat models, you should set their tokenizer.chat_template attribute and test it using
[~PreTrainedTokenizer.apply_chat_template], then push the updated tokenizer to the Hub. This applies even if you're
not the model owner - if you're using a model with an empty chat template, or one that's still using the default class
template, please open a pull request to the model repository so that this attribute can be set properly!
Once the attribute is set, that's it, you're done! tokenizer.apply_chat_template will now work correctly for that
model, which means it is also automatically supported in places like TextGenerationPipeline!
By ensuring that models have this attribute, we can make sure that the whole community gets to use the full power of
open-source models. Formatting mismatches have been haunting the field and silently harming performance for too long - 
it's time to put an end to them!
Advanced: Template writing tips
If you're unfamiliar with Jinja, we generally find that the easiest way to write a chat template is to first
write a short Python script that formats messages the way you want, and then convert that script into a template.
Remember that the template handler will receive the conversation history as a variable called messages.
You will be able to access messages in your template just like you can in Python, which means you can loop over 
it with {% for message in messages %} or access individual messages with {{ messages[0] }}, for example.
You can also use the following tips to convert your code to Jinja:
Trimming whitespace
By default, Jinja will print any whitespace that comes before or after a block. This can be a problem for chat
templates, which generally want to be very precise with whitespace! To avoid this, we strongly recommend writing
your templates like this:
{%- for message in messages %}
    {{- message['role'] + message['content'] }}
{%- endfor %}
rather than like this:
{% for message in messages %}
    {{ message['role'] + message['content'] }}
{% endfor %}
Adding - will strip any whitespace that comes before the block. The second example looks innocent, but the newline
and indentation may end up being included in the output, which is probably not what you want!
For loops
For loops in Jinja look like this:
{%- for message in messages %}
    {{- message['content'] }}
{%- endfor %}
Note that whatever's inside the {{ expression block }} will be printed to the output. You can use operators like
+ to combine strings inside expression blocks.
If statements
If statements in Jinja look like this:
{%- if message['role'] == 'user' %}
    {{- message['content'] }}
{%- endif %}
Note how where Python uses whitespace to mark the beginnings and ends of for and if blocks, Jinja requires you
to explicitly end them with {% endfor %} and {% endif %}.
Special variables
Inside your template, you will have access to the list of messages, but you can also access several other special
variables. These include special tokens like bos_token and eos_token, as well as the add_generation_prompt
variable that we discussed above. You can also use the loop variable to access information about the current loop
iteration, for example  using {% if loop.last %} to check if the current message is the last message in the 
conversation. Here's an example that puts these ideas together to add a generation prompt at the end of the
conversation if add_generation_prompt is True:
{%- if loop.last and add_generation_prompt %}
    {{- bos_token + 'Assistant:\n' }}
{%- endif %}