Improved error message when index in __getitem__() is invalid.

django/core/paginator.py

@@ -151,7 +151,10 @@ class Page(collections.abc.Sequence):
 
     def __getitem__(self, index):
         if not isinstance(index, (int, slice)):
-            raise TypeError
+            raise TypeError(
+                'Page indices must be integers or slices, not %s.'
+                % type(index).__name__
+            )
         # The object_list is converted to a list so that if it was a QuerySet
         # it won't be a database hit per __getitem__.
         if not isinstance(self.object_list, list):