title: Got an unexpected keyword argument 'pk'
body: <p>I have a list of Classes, and i need to get info of certain Class (i.e. student names, Class monitor etc). There is no problem in displaying Classes list (<code>localhost:8000/classes</code>), but when i'm addressing particular class (<code>localhost:8000/classes/nice_guys</code>), i receive <code>class_list() got an unexpected keyword argument 'pk' error</code>.</p>
  
  <p><strong>views.py</strong></p>
  
  <pre><code>def class_list(request):
      classes = Class.objects.all()
      return render(request, 'classes/class_list.html', {'classes': classes})
  
  def class_display(request, pk):
      class_to_display = get_object_or_404(Class, pk=pk)
      return render(request, 'classes/class_display.html', {'class_to_display': class_to_display})
  </code></pre>
  
  <p>application <strong>urls.py</strong></p>
  
  <pre><code>urlpatterns = [
      url(r'(?P&lt;pk&gt;\w+)', views.class_display),
      url(r'', views.class_list),
  ]
  </code></pre>
  
  <p>outer <strong>urls.py</strong></p>
  
  <pre><code>urlpatterns = [
      url(r'^admin/', admin.site.urls),
      url(r'^classes/(?P&lt;pk&gt;\w+)', include('students.urls')),
      url(r'^classes', include('students.urls')),
      url(r'^$', views.hello_world)
  ]
  </code></pre>