list.sort() and builtin.sorted() no longer accept 'cmp' argument.

Doc/whatsnew/3.0.rst

@@ -141,6 +141,10 @@ changes to rarely used features.)
   :meth:`dict.values` return views instead of lists.  For example, this no
   longer works: ``k = d.keys(); k.sort()``.  Use ``k = sorted(d)`` instead.
 
+* :meth:`builtin.sorted` and :meth:`list.sort` no longer accept the `cmp`
+  argument providing a comparision function.  Use the `key` argument
+  instead. N.B. the `key` and `reverse` arguments are now "keyword-only".
+
 * ``1/2`` returns a float.  Use ``1//2`` to get the truncating behavior.
 
 * The :func:`repr` of a long integer doesn't include the trailing ``L``