[python] Reverse for '*' with arguments '()' and keyword arguments '{}' not found

Caught an exception while rendering:

Reverse for 'products.views.'filter_by_led' with arguments '()' and keyword arguments '{}' not found.

I was able to successfully import products.views.filter_by_led from the shell and it worked so the path should be correct.

Here is the urls.py:

(r'^led-tv/$', filter_by_led ),

This is where the error is being generated:

href="{% url products.views.filter_by_led %}">

Which I can't understand because this works fine from the same file:

{% url products.views.lcd_screen_size screen_size=50 %}

Here is the function definition:

def filter_by_led(request):

I don't understand why Django would think that the function would not be able to find the Reverse for that function.

I deleted all the *.pyc files and restarted Apache.

What am I doing wrong?

Shell calls to reverse (as mentioned above) are very good to debug these problems, but there are two critical conditions:

• you must supply arguments that matches whatever arguments the view needs,
• these arguments must match regexp patterns.

Yes, it's logical. Yes, it's also confusing because reverse will only throw the exception and won't give you any further hints.

An example of URL pattern:

url(r'^cookies/(?P<hostname>[^/]+)/(?P<url_id>\d+)/$', 'register_site.views.show_cookies', name='show_cookies'),

And then what happens in shell:

>>> from register_site.views import show_cookies
>>> reverse(show_cookies)
NoReverseMatch: Reverse for 'register_site.views.show_cookies' with arguments '()' and keyword arguments '{}' not found.

It doesn't work because I supplied no arguments.

>>> reverse('show_cookies', kwargs={'url_id':123,'hostname': 'aaa'})
'/cookies/aaa/123'

Now it worked, but...

>>> reverse('show_cookies', kwargs={'url_id':'x','hostname': 'www.dupa.com'})
NoReverseMatch: Reverse for 'show_cookies' with arguments '()' and keyword arguments '{'url_id': 'x', 'hostname': 'www.dupa.com'}' not found.

Now it didn't work because url_id didn't match the regexp (expected numeric, supplied string).

You can use reverse with both positional arguments and keyword arguments. The syntax is:

reverse(viewname, urlconf=None, args=None, kwargs=None, prefix=None, current_app=None)

As it comes to the url template tag, there's funny thing about it. Django documentation gives example of using quoted view name:

{% url 'news.views.year_archive' yearvar %}

So I used it in a similar way in my HTML template:

{% url 'show_cookies' hostname=u.hostname url_id=u.pk %}

But this didn't work for me. But the exception message gave me a hint of what could be wrong - note the double single quotes around view name:

Reverse for ''show_cookies'' with arguments...

It started to work when I removed the quotes:

{% url show_cookies hostname=u.hostname url_id=u.pk %}

And this is confusing.

{% url 'polls:create' poll.id %}

In case it helps someone, I had a similar issue and the error was because of two reasons:

1. Not using the app's namespace before the url name

   {% url 'app_name:url_name' %}
   

2. Missing single quotes around the url name (as pointed out here by Charlie)

I don't think you need the trailing slash in the URL entry. Ie, put this instead:

(r'^led-tv$', filter_by_led ),

This is assuming you have trailing slashes enabled, which is the default.

I had a similar problem and the solution was in the right use of the '$' (end-of-string) character:

My main url.py looked like this (notice the $ character):

urlpatterns = [
url(r'^admin/', include(admin.site.urls )),
url(r'^$', include('card_purchase.urls' )),
]

and my url.py for my card_purchases app said:

urlpatterns = [
url(r'^$', views.index, name='index'),
url(r'^purchase/$', views.purchase_detail, name='purchase')
]

I used the '$' twice. So a simple change worked:

urlpatterns = [
url(r'^admin/', include(admin.site.urls )),
url(r'^cp/', include('card_purchase.urls' )),
]

Notice the change in the second url! My url.py for my card_purchases app looks like this:

urlpatterns = [
url(r'^$', views.index, name='index'),
url(r'^purchase/$', views.purchase_detail, name='purchase')
]

Apart from this, I can confirm that quotes around named urls are crucial!

You need single quotes around the view name

{% url 'viewname' %}

instead of

{% url viewname %}