Coffin: Jinja2 adapter for Django

Supported Django template functionality

Coffin currently makes the following Django tags available in Jinja:

• {% cache %} - has currently an incompatibility: The second argument (the fragment name) needs to be specified with surrounding quotes if it is supposed to be a literal string, according to Jinja2 syntax. It will otherwise be considered an identifer and resolved as a variable.
• {% load %} - is actually a no-op in Coffin, since templatetag libraries are always loaded. See also "Custom Filters and extensions".
• {% spaceless %}
• {% url %} - additionally, a "view"|url() filter is also available.
• {% with %}
• {% csrf_token %}

Django filters that are ported in Coffin:

• date
• floatformat
• pluralize (expects an optional second parameter rather than the comma syntax)
• time
• timesince
• timeuntil
• truncatewords
• truncatewords_html

Note that for the most part, you can simply use filters written for Django directly in Coffin. For example, django.contrib.markup "just works" (tm).

The template-related functionality of the following contrib modules has been ported in Coffin:

• coffin.contrib.syndication.

Jinja 2's i18n extension is hooked up with Django, and a custom version of makemessages supports string extraction from both Jinja2 and Django templates.

Autoescape

When using Auto Escape you will notice that marking something as a Safestrings with Django will not affect the rendering in Jinja 2. To fix this you can monkeypatch Django to produce Jinja 2 compatible Safestrings:

'''Monkeypatch Django to mimic Jinja2 behaviour'''
from django.utils import safestring
if not hasattr(safestring, '__html__'):
    safestring.SafeString.__html__ = lambda self: str(self)
    safestring.SafeUnicode.__html__ = lambda self: unicode(self)

Rendering

Change the TEMPLATE_LOADERS settings to contain only the following loader:

TEMPLATE_LOADERS = (
   'coffin.template.loaders.Loader',
)

And move all previously defined template loaders to the JINJA2_TEMPLATE_LOADERS setting directive:

JINJA2_TEMPLATE_LOADERS = (
    'django.template.loaders.app_directories.Loader',
    'django.template.loaders.filesystem.Loader',
)

From now on, all of your views, generic views and error pages will be handled and rendered by Jinja2.

Using the django rendering engine

If your project uses some applications which needs to original django templating engine to correctly render their templates, you can add their names to a JINJA2_DISABLED_TEMPLATES setting and coffin will render the templates using the django templating engine.

If you use the built-in admin app, you have then to add the following setting:

JINJA2_DISABLED_TEMPLATES = (
  'admin',
)

Each entry in the JINJA2_DISABLED_TEMPLATES iterable is treated as a regex pattern and every template is tested against them to check if it has to be rendered using Jinja+Coffin or with the built-in templating engine.

You can define the settings as shown in the following example:

JINJA2_DISABLED_TEMPLATES = (
  r'[^/]+\.html',                           # All generic templates
  r'myapp/(registration|photos|calendar)/', # The three apps in the myapp package
  r'auth/',                                 # All auth templates
  r'(cms|menu|admin|admin_doc)/',           # The templates of these 4 apps
)

404 and 500 handlers

To have your HTTP 404 and 500 template rendered using Jinja, replace the line:

from django.conf.urls.defaults import *

in your urls.py (it should be there by default), with:

from coffin.conf.urls.defaults import *

Custom filters and extensions

Coffin uses the same templatetag library approach as Django, meaning your app has a templatetags directory, and each of it's modules represents a "template library", providing new filters and tags.

A custom Library class in coffin.template.Library can be used to register Jinja-specific components.

Coffin can automatically make your existing Django filters usable in Jinja, but not your custom tags - you need to rewrite those as Jinja extensions manually.

Example for a Jinja-enabled template library:

from coffin import template
register = template.Library()

register.filter('plenk', plenk)   # Filter for both Django and Jinja
register.tag('foo', do_foo)       # Django version of the tag
register.tag(FooExtension)        # Jinja version of the tag
register.object(my_function_name) # A global function/object
register.test(my_test_name)       # A test function

You may also define additional extensions, filters, tests and globals via your settings.py:

JINJA2_FILTERS = (
    'path.to.myfilter',
)
JINJA2_TESTS = {
    'test_name': 'path.to.mytest',
}
JINJA2_EXTENSIONS = (
    'jinja2.ext.do',
)

Other things of note

When porting Django functionality, Coffin currently tries to avoid Django's silent-errors approach, instead opting to be explicit. Django was discussing the same thing before it's 1.0 release (*), but was constrained by backwards-compatibility concerns. However, if you are converting your templates anyway, it might be a good opportunity for this change.

(*) http://groups.google.com/group/django-developers/browse_thread/thread/f323338045ac2e5e

coffin.template.loader is a port of django.template.loader and comes with a Jinja2-enabled version of get_template().

coffin.template.Template is a Jinja2-Template that supports the Django render interface (being passed an instance of Context), and uses Coffin's global Jinja2 environment.

coffin.interop exposes functionality to manually convert Django filters to Jinja2 and vice-versa. This is also what Coffin's Library object uses.

A Jinja2-enabled version of add_to_builtins can be found in the django.template namespace.

You may specify additional arguments to send to the Environment via JINJA2_ENVIRONMENT_OPTIONS:

from jinja2 import StrictUndefined
JINJA2_ENVIRONMENT_OPTIONS = {
    'autoescape': False,
    'undefined': StrictUndefined,
}

Things not supported by Coffin

These is an incomplete list things that Coffin does not yet and possibly never will, requiring manual changes on your part:

• The slice filter works differently in Jinja2 and Django. Replace it with Jinja's slice syntax: x[0:1].
• Jinja2's default filter by itself only tests the variable for existance. To match Django's behaviour, you need to pass True as the second argument, so that it will also provide the default value for things that are defined but evalute to False
• Jinja2's loop variable is called loop, but Django's forloop.
• Implementing an equivalent to Django's cycle-tag might be difficult, see also Django tickets #5908 and #7501. Jinja's own facilities are the forloop.cycle() function and the global function cycler.
• The add filter might not be worth being implemented. {{ x+y }} is a pretty basic feature of Jinja2, and could almost be lumped together with the other Django->Jinja2 syntax changes.
• Django-type safe strings passed through the context are not converted and therefore not recognized by Jinja2. For example, a notable place were this would occur is the HTML generation of Django Forms.
• The {% autoescape %} tag is immensily difficult to port and currently not supported.
• Literal strings from within a template are not automatically considered "safe" by Jinja2, different from Django. According to Armin Ronacher, this is a design limitation that will not be changed, due to many Python builtin functions and methods, whichyou are free to use in Jinja2, expecting raw, untainted strings and thus not being able to work with Jinja2's Markup string.

Running the tests

Use the nose framework:

http://somethingaboutorange.com/mrl/projects/nose/