old_contents: from django.conf.urls import url
  
  from . import views
  
  urlpatterns = [
      url(r'^$', views.index, name='index'),
      url(r'^locations/?(?P<id>[0-9]+)?$',views.location, name='location'),
  ]
  
new_contents: from django.conf.urls import url
  
  from . import views
  
  urlpatterns = [
      url(r'^$', views.index, name='index'),
      url(r'^locations/?(?P<id>[0-9]+)?$',views.location, name='location'),
      url(r'^categories/?(?P<id>[0-9]+)?$',views.category, name='category'),
  ]
  
subject: Add url for category