``Py_NotImplemented``, if another error occurred it must return *NULL* and
set an exception condition.
- .. note::
-
- If you want to implement a type for which only a limited set of
- comparisons makes sense (e.g. ``==`` and ``!=``, but not ``<`` and
- friends), directly raise :exc:`TypeError` in the rich comparison function.
-
The following constants are defined to be used as the third argument for
:c:member:`~PyTypeObject.tp_richcompare` and for :c:func:`PyObject_RichCompare`: