Change len() to .count() for check

website/events/views.py

@@ -233,7 +233,7 @@ def registration(request, event_id, action=None):
             if (obj is not None and
                     obj.date_cancelled is None):
                 if (event.max_participants is not None and
-                        len(Registration.objects.filter(event=event)) >=
+                        Registration.objects.filter(event=event).count() >=
                         event.max_participants):
                     # Prepare email to send to the first person on the waiting
                     # list