The "None" Object
*****************

Note that the "PyTypeObject" for "None" is not directly exposed in the
Python/C API.  Since "None" is a singleton, testing for object
identity (using "==" in C) is sufficient. There is no "PyNone_Check()"
function for the same reason.

PyObject* Py_None

   The Python "None" object, denoting lack of value.  This object has
   no methods. It needs to be treated just like any other object with
   respect to reference counts.

Py_RETURN_NONE

   Properly handle returning "Py_None" from within a C function.

   2.4 版新加入.
