Unable to reverse URL

[Vincent]

Hi everyone,

I've started working on an application after some trime, but I can not get it to run again.

I've got this error:

  Reverse for '' with arguments '()' and keyword arguments '{}' not found. 0 pattern(s) tried: []

Internal Server Error: /substances/
Traceback (most recent call last):
  File "C:\Python27\lib\site-packages\django\core\handlers\base.py", line 164, in get_response
    response = response.render()
  File "C:\Python27\lib\site-packages\django\template\response.py", line 158, in render
    self.content = self.rendered_content
  File "C:\Python27\lib\site-packages\django\template\response.py", line 135, in rendered_content
    content = template.render(context, self._request)
  File "C:\Python27\lib\site-packages\django\template\backends\django.py", line 74, in render
    return self.template.render(context)
  File "C:\Python27\lib\site-packages\django\template\base.py", line 209, in render
    return self._render(context)
  File "C:\Python27\lib\site-packages\django\template\base.py", line 201, in _render
    return self.nodelist.render(context)
  File "C:\Python27\lib\site-packages\django\template\base.py", line 903, in render
    bit = self.render_node(node, context)
  File "C:\Python27\lib\site-packages\django\template\debug.py", line 79, in render_node
    return node.render(context)
  File "C:\Python27\lib\site-packages\django\template\loader_tags.py", line 135, in render
    return compiled_parent._render(context)
  File "C:\Python27\lib\site-packages\django\template\base.py", line 201, in _render
    return self.nodelist.render(context)
  File "C:\Python27\lib\site-packages\django\template\base.py", line 903, in render
    bit = self.render_node(node, context)
  File "C:\Python27\lib\site-packages\django\template\debug.py", line 79, in render_node
    return node.render(context)
  File "C:\Python27\lib\site-packages\django\template\defaulttags.py", line 329, in render
    return nodelist.render(context)
  File "C:\Python27\lib\site-packages\django\template\base.py", line 903, in render
    bit = self.render_node(node, context)
  File "C:\Python27\lib\site-packages\django\template\debug.py", line 79, in render_node
    return node.render(context)
  File "C:\Python27\lib\site-packages\django\template\defaulttags.py", line 507, in render
    six.reraise(*exc_info)
  File "C:\Python27\lib\site-packages\django\template\defaulttags.py", line 493, in render
    url = reverse(view_name, args=args, kwargs=kwargs, current_app=current_app)
  File "C:\Python27\lib\site-packages\django\core\urlresolvers.py", line 579, in reverse
    return force_text(iri_to_uri(resolver._reverse_with_prefix(view, prefix, *args, **kwargs)))
  File "C:\Python27\lib\site-packages\django\core\urlresolvers.py", line 496, in _reverse_with_prefix
    (lookup_view_s, args, kwargs, len(patterns), patterns))
NoReverseMatch: Reverse for '' with arguments '()' and keyword arguments '{}' not found. 0 pattern(s) tried: []
[13/Jul/2015 15:32:02]"GET /substances/ HTTP/1.1" 500 185051

It happens when it encounters the first reverse lookup:

   <li><a href=" {% url substance_list %} ">Stubstances</a></li>

I've traced it down to the render method in the URLNode class (in defaulttags), where

    view_name = self.view_name.resolve(context)

returns an empty string.

I have the following URL configurations

site urls.py:

urlpatterns = (
    url(r'^$', lambda r : HttpResponseRedirect('substances/')),
    url(r'^norights/', TemplateView.as_view(template_name="norights.html"), name="norights"),
    url(r'^substances/',    include('substances.urls')),
    url(r'^suppliers/',     include('suppliers.urls')),
    url(r'^users/',         include('users.urls')),
    url(r'^sources/',       include('sources.urls')),
    url(r'^media/(.*)$', 'django.views.static.serve', {'document_root' :settings.MEDIA_ROOT}, name="media"),
)

app urls.py

urlpatterns = (
    url(r'^$', SubstanceListView.as_view(),                         name = 'substance_list'),
    url(r'^create$', SubstanceCreateView.as_view(),                 name = 'substance_create'),
    url(r'^update/(?P<pk>\d+)$', SubstanceUpdateView.as_view(),     name = 'substance_update'),
    url(r'^detail/(?P<pk>\d+)$', SubstanceDetailView.as_view(),     name = 'substance_detail'),
    url(r'^mutate/(?P<pk>\d+)$', SubstanceMutateView.as_view(),     name = 'substance_mutate'),
    url(r'^delete/(?P<pk>\d+)$', SubstanceDeleteView.as_view(),     name = 'substance_delete'),
   
    url(r'^mutate_check_ajax/(?P<pk>\d+)$', mutate_check_ajax,      name = 'mutate_check_ajax'),
    url(r'^component_check_ajax$', component_check_ajax,            name = 'component_check_ajax'),
    url(r'^supplier_check_ajax$', supplier_check_ajax,              name = 'supplier_check_ajax'),
    url(r'^report', substance_report,                               name = 'substance_report'),
    url(r'^worksheet/(?P<pk>\d+)$', substance_worksheet,            name = 'substance_worksheet')
)

Oddly enough I did not change anything to get the error. Afterwards I upgraded to Django 1.8.3, but that did not matter.



Thanks,
Vincent

[James Schneider]

What is the value being given to substance_list in your template context? It looks like it may be empty.

Unless 'substance_list' is the actual name of the view? In which case you probably need to add quotes around it in your URL tag:

{% url 'substance_list' %} 

As is it is, the template is reading substance_list as a variable. If it is the name, and not a variable, I would suggest looking into Django URL name spaces, which are much easier to diagnose and maintain, and avoid the missing quote issue since there can never be a variable name containing the : character. For example,

{% url 'substance:list' %} 

Is much less vague than 'substance_list' since the : version wouldn't also work as a variable name, making it easier to figure out that you want the name of a URL and not a variable name.

https://docs.djangoproject.com/en/1.8/topics/http/urls/#url-namespaces

-James

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[Vincent]

Hi James,

substance_list is indeed the name of the view. I've now applied namespaces, and added quotes around each URL statement, and it works! thanks!

What I do not understand is how it could have worked in the past.

Regards,
Vincent

[James Schneider]

That particular syntax works in Django 1.4, did you do an upgrade?

-James

To view this discussion on the web visit https://groups.google.com/d/msgid/django-users/bde30363-a061-482d-8226-501097f83d2c%40googlegroups.com.