Document how to reverse URL patterns with nested groups

[Nick Retallack]

## urls.py
from django.conf.urls.defaults import *
from django.http import HttpResponse

urlpatterns = patterns('',
    url(r'^export1\.(?P<format>\w+)$', lambda request: HttpResponse("THIS"), name='this'),
    url(r'^export2(\.(?P<format>\w+))?$', lambda request: HttpResponse("THAT"), name='that'),
)

## paste into python manage.py shell

from django.core.urlresolvers import reverse, resolve

# Both urls resolve
resolve('/export1.json')[0](None).content
resolve('/export2.json')[0](None).content

# These reverse
reverse('this', args=['json'])
reverse('this', kwargs={'format':'json'})

# These don't
reverse('that', args=['json'])
reverse('that', kwargs={'format':'json'})

## Shell session output

>>> from django.core.urlresolvers import reverse, resolve
>>> 
>>> # Both urls resolve
>>> resolve('/export1.json')[0](None).content
'THIS'
>>> resolve('/export2.json')[0](None).content
'THAT'
>>> 
>>> # These reverse
>>> reverse('this', args=['json'])
'/export1.json'
>>> reverse('this', kwargs={'format':'json'})
'/export1.json'
>>> 
>>> # These don't
>>> reverse('that', args=['json'])
Traceback (most recent call last):
  File "<console>", line 1, in <module>
  File "/usr/local/Cellar/python/2.6.4/lib/python2.6/site-packages/django/core/urlresolvers.py", line 350, in reverse
    *args, **kwargs)))
  File "/usr/local/Cellar/python/2.6.4/lib/python2.6/site-packages/django/core/urlresolvers.py", line 300, in reverse
    "arguments '%s' not found." % (lookup_view_s, args, kwargs))
NoReverseMatch: Reverse for 'that' with arguments '('json',)' and keyword arguments '{}' not found.

[Russell Keith-Magee]

I have a suspicion that this will be difficult to fix; if it can't be fixed, it should certainly be documented as a limitation.

[3point2]

i just bumped my head against this limitation, it would be great if there was a fix.

[Aymeric Augustin]

Change UI/UX from NULL to False.

[Aymeric Augustin]

Change Easy pickings from NULL to False.

[Bas Peschier]

This is very hard to do, since both groups are captured and (if there was a working implementation) should both be given to the reverser. There would be a hard link between both groups since the inner group would influence the outer group. Using an outer non-capturing group will work and is recommended for this use case:

urlpatterns = patterns('',
    url(r'^export1\.(?P<format>\w+)$', lambda request: HttpResponse("THIS"), name='this'),
    url(r'^export2(?:\.(?P<format>\w+))?$', lambda request: HttpResponse("THAT"), name='that'),
)

I can update the tests and document the limitations that nested captured groups are not supported.

[Bas Peschier]

​https://github.com/django/django/pull/4353

[Tim Graham]

Looks good, pending some cosmetic comments.

[Tim Graham <timograham@…>]

In 23a5d64f:

Fixed #13525 -- Added tests and docs for nested parameters in URL patterns.

When reversing, only outer parameters are used if captured parameters are
nested. Added tests to check the edge cases and documentation for the
behavior with an example to avoid it.

[Tim Graham <timograham@…>]

In 015a9b9:

[1.8.x] Fixed #13525 -- Added tests and docs for nested parameters in URL patterns.

When reversing, only outer parameters are used if captured parameters are
nested. Added tests to check the edge cases and documentation for the
behavior with an example to avoid it.

Backport of 23a5d64f40b0f4a3fbfef7427ca793cb1df1034e from master