#9166: NotImplemented is not an exception.

Doc/whatsnew/2.7.rst

@@ -1072,7 +1072,7 @@ changes, or look through the Subversion logs for all the details.
   (Added by Raymond Hettinger; :issue:`1818`.)
 
   Finally, the :class:`~collections.Mapping` abstract base class now
-  raises a :exc:`NotImplemented` exception if a mapping is compared to
+  returns :const:`NotImplemented` if a mapping is compared to
   another type that isn't a :class:`Mapping`.
   (Fixed by Daniel Stutzbach; :issue:`8729`.)