Improved generic detail view error message for when pk or slug is missing.

django/views/generic/detail.py

@@ -42,9 +42,10 @@ class SingleObjectMixin(ContextMixin):
 
         # If none of those are defined, it's an error.
         if pk is None and slug is None:
-            raise AttributeError("Generic detail view %s must be called with "
-                                 "either an object pk or a slug."
-                                 % self.__class__.__name__)
+            raise AttributeError(
+                "Generic detail view %s must be called with either an object "
+                "pk or a slug in the URLconf." % self.__class__.__name__
+            )
 
         try:
             # Get the single item from the filtered queryset

tests/generic_views/test_dates.py

@@ -695,7 +695,11 @@ class DateDetailViewTests(TestDataMixin, TestCase):
                 self.assertEqual(res.context['exception'], 'Date out of range')
 
     def test_invalid_url(self):
-        with self.assertRaises(AttributeError):
+        msg = (
+            'Generic detail view BookDetail must be called with either an '
+            'object pk or a slug in the URLconf.'
+        )
+        with self.assertRaisesMessage(AttributeError, msg):
             self.client.get("/dates/books/2008/oct/01/nopk/")
 
     def test_get_object_custom_queryset(self):