Regular expression in URL for Django slug

I believe that you can also drop the _ from the pattern that @Ludwik has suggested and revise to this version (which is one character simpler :) ):

url(r'^genres/(?P<slug>[-\w]+)/$', views.genre_view, name='genre_view'),
url(r'^genres/(?P<slug>[-\w]+)/monthly/$', views.genre_month, name='genre_month'),

Note that \w stands for "word character". It always matches the ASCII characters [A-Za-z0-9_]. Notice the inclusion of the underscore and digits. more info

Django always uses the first pattern that matches. For urls similar to genres/genre_name/monthly your first pattern matches, so the second one is never used. The truth is the regex is not specific enough, allowing all characters - which doesn't seem to make sense.

You could reverse the order of those patterns, but what you should do is to make them more specific (compare: urls.py example in generic class-based views docs):

url(r'^genres/(?P<slug>[-\w]+)/$', views.genre_view, name='genre_view'),
url(r'^genres/(?P<slug>[-\w]+)/monthly/$', views.genre_month, name='genre_month'),

Edit 2020:

Those days (since Django 2.0), you can (and should) use path instead of url. It provides built-in path converters, including slug:

path('genres/<slug:slug>/', views.genre_view, name='genre_view'),
path('genres/<slug:slug>/monthly/', views.genre_month, name='genre_month'),