Merge with 3.4

Doc/library/functions.rst

@@ -742,7 +742,8 @@ are always available.  They are listed here in alphabetical order.
 .. 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 (such as a string, bytes, tuple, list, or range) or a collection
+   (such as a dictionary, set, or frozen set).
 
 
 .. _func-list:

Python/bltinmodule.c

@@ -1327,7 +1327,7 @@ builtin_len(PyObject *self, PyObject *v)
 PyDoc_STRVAR(len_doc,
 "len(object)\n\
 \n\
-Return the number of items of a sequence or mapping.");
+Return the number of items of a sequence or collection.");
 
 
 static PyObject *