Receiving NoReverseMatch using {% url %} and Generic Views

[Bryan Veloso]

My project uses only generic views with named URL patterns. After updating to [8317] tonight, I ran into an error probably related to the [8211] NoReverseMatch exception change. Before the update, my {% url %} tags, which consist of only a single argument, e.g. {% url project-list %} return the following error:

Traceback (most recent call last):, referer: http://djangoplugables.com/
  File "/usr/lib/python2.5/site-packages/django/core/handlers/wsgi.py", line 216, in __call__, referer: http://djangoplugables.com/
    response = self.get_response(request), referer: http://djangoplugables.com/
  File "/usr/lib/python2.5/site-packages/django/core/handlers/base.py", line 125, in get_response, referer: http://djangoplugables.com/
    return self.handle_uncaught_exception(request, resolver, exc_info), referer: http://djangoplugables.com/
  File "/usr/lib/python2.5/site-packages/django/core/handlers/base.py", line 157, in handle_uncaught_exception, referer: http://djangoplugables.com/
    return callback(request, **param_dict), referer: http://djangoplugables.com/
  File "/usr/lib/python2.5/site-packages/django/views/defaults.py", line 89, in server_error, referer: http://djangoplugables.com/
    return http.HttpResponseServerError(t.render(Context({}))), referer: http://djangoplugables.com/
  File "/usr/lib/python2.5/site-packages/django/template/__init__.py", line 176, in render, referer: http://djangoplugables.com/
    return self.nodelist.render(context), referer: http://djangoplugables.com/
  File "/usr/lib/python2.5/site-packages/django/template/__init__.py", line 751, in render, referer: http://djangoplugables.com/
    bits.append(self.render_node(node, context)), referer: http://djangoplugables.com/
  File "/usr/lib/python2.5/site-packages/django/template/__init__.py", line 764, in render_node, referer: http://djangoplugables.com/
    return node.render(context), referer: http://djangoplugables.com/
  File "/usr/lib/python2.5/site-packages/django/template/loader_tags.py", line 97, in render, referer: http://djangoplugables.com/
    return compiled_parent.render(context), referer: http://djangoplugables.com/
  File "/usr/lib/python2.5/site-packages/django/template/__init__.py", line 176, in render, referer: http://djangoplugables.com/
    return self.nodelist.render(context), referer: http://djangoplugables.com/
  File "/usr/lib/python2.5/site-packages/django/template/__init__.py", line 751, in render, referer: http://djangoplugables.com/
    bits.append(self.render_node(node, context)), referer: http://djangoplugables.com/
  File "/usr/lib/python2.5/site-packages/django/template/__init__.py", line 764, in render_node, referer: http://djangoplugables.com/
    return node.render(context), referer: http://djangoplugables.com/
  File "/usr/lib/python2.5/site-packages/django/template/defaulttags.py", line 29, in render, referer: http://djangoplugables.com/
    output = self.nodelist.render(context), referer: http://djangoplugables.com/
  File "/usr/lib/python2.5/site-packages/django/template/__init__.py", line 751, in render, referer: http://djangoplugables.com/
    bits.append(self.render_node(node, context)), referer: http://djangoplugables.com/
  File "/usr/lib/python2.5/site-packages/django/template/__init__.py", line 764, in render_node, referer: http://djangoplugables.com/
    return node.render(context), referer: http://djangoplugables.com/
  File "/usr/lib/python2.5/site-packages/django/template/defaulttags.py", line 369, in render, referer: http://djangoplugables.com/
    args=args, kwargs=kwargs), referer: http://djangoplugables.com/
  File "/usr/lib/python2.5/site-packages/django/core/urlresolvers.py", line 307, in reverse, referer: http://djangoplugables.com/
    *args, **kwargs))), referer: http://djangoplugables.com/
  File "/usr/lib/python2.5/site-packages/django/core/urlresolvers.py", line 291, in reverse, referer: http://djangoplugables.com/
    raise NoReverseMatch("Reverse for '%s' not found." % lookup_view), referer: http://djangoplugables.com/
NoReverseMatch: Reverse for 'settings.project-list' not found., referer: http://djangoplugables.com/

What bugs me here is that it is looking in settings.project-list. Why would it be looking in the settings for a named URL argument? I was told that this could be a bug and I am reporting it as such. Please do not complicate matters by trying to find something more complex. I am merely using generic views and named arguments, and I am receiving these errors.

[Julien Phalip]

We'd need a bit more info to debug this. Could you post your URLConf and views? Even better would be a test case reproducing the issue.

[Malcolm Tredinnick]

It looks like the error is just being misreported, but it's still an error. If you look at the code in question (the changes in [8211]), you'll see that if a named pattern match fails, it then makes a final attempt to do "project name + function name" (for better or worse). Since you're not running in a project situation (it looks like your settings value is just settings here), the final step tries a project name of "settings". That's invalid, but it indicates that you've already failed to have a pattern match.

So it looks like some more care is needed with the error message construction here and that seems to be the way to resolve this ticket.

You don't indicate whether the {% url ... %} call in question worked (in the sense of "actually matched a pattern") previously or not. Looking at the changes in [8211] and where the exception is raised, I'd guess that it returned the empty string before, which is a result of not matching anything. If so, raising an error of some kind there is consistent with the intended effect of [8211].

[floguy]

This error is coming from the open source DjangoPlugables codebase.

The template in question is ​http://github.com/revyver/django-plugables/tree/master/templates/base.html

The URL that it should map to is: ​http://github.com/revyver/django-plugables/tree/master/applications/projects/urls.py

I was trying to go through and debug this error myself, but couldn't see why it should be failing. On twitter, Brian Rosner mentioned that he believes it could be related to #8246

[Brian Rosner]

It is late and I saw an exception and the word settings. It was simply a shot in the dog FWIW ;)

[floguy]

Replying to brosner:

It is late and I saw an exception and the word settings. It was simply a shot in the dog FWIW ;)

Oh please tell me you didn't shoot your dog.

[Bryan Veloso]

@Malcolm: I didn't? Hah, late and distressed I guess. But yes, to back up Eric, it DID work previously.

[Brian Rosner]

I haven't been able to track this down precisely yet, but what I have discovered can be useful. This exception only occurs when DEBUG is False. When DEBUG is True the real error is shown which was a third party app still using newforms references. Somehow this is getting masked.

[anonymous]

when i wite {% url django.contrib.auth.views.login %} in template, django show me error Caught an exception while rendering: Reverse for 'my_project.contrib.auth.views.login' not found.

Why it appends my_project? Is it a bug?

[anonymous]

Replying to anonymous:

when i wite {% url django.contrib.auth.views.login %} in template, django show me error Caught an exception while rendering: Reverse for 'my_project.contrib.auth.views.login' not found.

Why it appends my_project? Is it a bug?

Oh, sorry, the error is Caught an exception while rendering: Reverse for 'my_project.django.contrib.auth.views.login' not found.

[James Bennett]

Replying to brosner:

I haven't been able to track this down precisely yet, but what I have discovered can be useful. This exception only occurs when DEBUG is False. When DEBUG is True the real error is shown which was a third party app still using newforms references. Somehow this is getting masked.

If that's the case, this is a dupe of #7524.

[Jacob]

Milestone 1.0 deleted