eryksun added the comment: In Python 2 [Py_InitModule4][1] optionally allows setting __self__ on module functions, but no module in the standard library actually uses this. It's always None. This is no longer optional with Python 3's [PyModule_Create][2]. Built-in module functions instantiated the normal way can be considered as methods of the module in which they're defined. However, some modules may specially instantiate functions for which __self__ is None, such as codecs.strict_errors. >>> codecs.strict_errors.__self__ is None True [1]: https://docs.python.org/2/c-api/allocation.html#c.Py_InitModule4 [2]: https://docs.python.org/3/c-api/module.html#c.PyModule_Create ---------- nosy: +eryksun _______________________________________ Python tracker <report@bugs.python.org> <http://bugs.python.org/issue14003> _______________________________________