diff -r 179a3cf73e47 Doc/library/functions.rst
--- a/Doc/library/functions.rst	Tue Oct 22 23:26:23 2013 -0700
+++ b/Doc/library/functions.rst	Wed Oct 23 13:20:54 2013 +0100
@@ -727,7 +727,7 @@
 .. function:: len(s)
 
    Return the length (the number of items) of an object.  The argument may be a
-   sequence (string, tuple or list) or a mapping (dictionary).
+   sequence (string, tuple or list), a mapping (dictionary), or a set.
 
 
 .. _func-list:
diff -r 179a3cf73e47 Python/bltinmodule.c
--- a/Python/bltinmodule.c	Tue Oct 22 23:26:23 2013 -0700
+++ b/Python/bltinmodule.c	Wed Oct 23 13:20:54 2013 +0100
@@ -1304,7 +1304,7 @@
 PyDoc_STRVAR(len_doc,
 "len(object) -> integer\n\
 \n\
-Return the number of items of a sequence or mapping.");
+Return the number of items of a sequence, a mapping, or a set.");
 
 
 static PyObject *