#9176: NoReverseMatch for optional arguments
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Reporter: [EMAIL PROTECTED] | Owner: nobody
Status: new | Milestone:
Component: Core framework | Version: 1.0
Keywords: | Stage: Unreviewed
Has_patch: 0 |
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A number of URLs of my site have the form /<object_name>/something. The
objects can have several representations, one of which is canonical, so I
have a decorator that redirects requests with non-canonical names. The
decorator (simplified) looks like this:
{{{
def url_from_view(view, **kwargs):
return django.core.urlresolvers.reverse(view, kwargs=kwargs)
def decorator(view):
def wrapper(request, obj_name, **kwargs):
obj = load_object(obj_name)
if canonical_name(obj) != obj_name:
return HttpResponseRedirect(url_from_view(wrapper,
obj_name=canonical_name(obj), **kwargs)
return view(request, obj, obj_name, **kwargs)
return wrapper
}}}
Everything worked excellently, until I added something like this to my
urlpatterns:
{{{
(r"^(?P<parent>[a-zA-Z0-9_-])/something(?:/(?P<child>\d+))?/*$",
something),
}}}
For /parent_noncanonical/something/42 it calls
something(parent="parent_noncanonical", child="42") which then reverses
the URL and redirects correctly to /parent_canonical/something/42.
However, if the child part is omitted, because it’s optional in the regex,
as in /parent_noncanonical/something, the view gets called as
something(parent="parent_noncanonical", child=None) which then fails to
reverse.
The problem is that the reverse operation turns out not to be defined for
some of data that the regular expressions can produce: when I pass it the
same view and the same data that have been chosen by the urlpatterns, it
fails to produce a reverse match.
The reverse matching engine should handle None parameters by finding
matches which do not contain the corresponding groups. For example, for
r"(?P<first>[a-z])?(?P<second>[0-9])?(?P<third>[A-Z])?" and first="d",
second=None, third="J" the correct reverse match is "dJ".
Here’s the relevant Django code (core/urlresolvers.py, 227–241):
{{{
for result, params in possibilities:
if args:
# skipped
else:
if set(kwargs.keys()) != set(params):
continue
unicode_kwargs = dict([(k, force_unicode(v)) for (k, v) in
kwargs.items()])
candidate = result % unicode_kwargs
if re.search(u'^%s' % pattern, candidate, re.UNICODE):
return candidate
raise NoReverseMatch("Reverse for '%s' with arguments '%s' and
keyword "
"arguments '%s' not found." % (lookup_view, args, kwargs))
}}}
For the URL pattern above, the possibilities are correctly enumerated:
[(u'%(parent)s/something', ['parent']),
(u'%(parent)s/something/%(child)s', ['parent', 'child'])]
But then it fails to take into account the fact child is None, and chooses
the wrong possibility.
Perhaps simply eliminating None by changing set(kwargs.keys()) !=
set(params) to set([k for (k, v) in kwargs.items() if v]) != set(params)
could do the job.
--
Ticket URL: <http://code.djangoproject.com/ticket/9176>
Django <http://code.djangoproject.com/>
The Web framework for perfectionists with deadlines.
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