Cannot pickle the default filters

[simon@…]

Reproduction code:

from django import template
t = template.Template("{{ firstname|capfirst }}")
c = template.Context("firstname": "simon")
p = pickle.dumps(t)
print pickle.loads(p).render(c)

Expected result:

Simon

Actual result:

<class 'pickle.PicklingError'>: Can't pickle <function _dec at 0x83c010c>: it's not found as django.template.defaultfilters._dec

[simon@…]

Patch

[Malcolm Tredinnick]

The __name__ attribute is write-only in Python 2.3.

This might be fixed by Jeremy Dunck's recent decorator work (which isn't going in just yet because we need to get some license clearance).

We're probably unlikely to jump through a lot of hoops to make pickling work, though, if more than this is required.

[Simon Law <simon@…>]

I see. This is related to #3558.

Since name is read-only in Python 2.3, it still possible for this to work by wrapping the patch in a try statement.

try:
    _dec.__name__ = func.__name__ 
except TypeError:
    pass

This breaks pickling in Python 2.3, but permits it elsewhere.

Pickling is useful so that we can cache templates in memcached. If template parsing is non-trivial, you really want to cache these objects.

[Jacob]

As Malcolm said, this is a duplicate of #5701.