Document which template filters can be used in Python code (and how)

[Baptiste Mispelon]

The Django template language ships with a lot of filters. Usually they're implemented as Python functions and can be imported and used in your own code.

However this particular usage is not documented (take the example of the various truncate* filters [1]).

I think it would be useful to know:

1) Which template filters can be used as functions;
2) Where to import them from and how to use them;
3) If there are limitations/gotchas related to using them.

[1] ​https://docs.djangoproject.com/en/1.10/ref/templates/builtins/#truncatechars

[Tim Graham]

While I think I've imported from django.template.defaultfilters in some of my own projects, I'm not sure that promoting that pattern as a public API is a good idea. Some of the filters use functions from django.utils.*, e.g. the slugify filter uses django.utils.text.slugify. I don't mind linking to those utility functions from the template tag documentation.

[Aymeric Augustin]

Yes, generally speaking Django template filters should be thin wrappers about utility functions. This makes it easy to use the underlying plain function in Jinja2 templates.

[Burhan Khalid]

I'll work a PR for this, where I'll link to the relevant django.utils.* documentation for those filters that are pure wrappers for other functions.

[Burhan Khalid]

​https://github.com/django/django/pull/7519

There was some documentation missing for some of the utils functions, which I added to the relevant sections in order to ensure Sphinx internal references were linked correctly.