Question

I have this module, wat.py

import re
import types
import sys

hello = "Hello World"

class MyModule(types.ModuleType):
    def get_re(self):
        return re
    def get_hello(self):
        return hello


sys.modules[__name__] = MyModule('wat')

And I run this code:

>>> import wat
>>> wat.get_hello()
None
>>> wat.get_re()
None

Why does this not work?

Answer 1

It doesn’t work because you effectively deleted your module when you reassigned its entry in sys.modules. See my related question.

To make it work, change the last line of your module to:

_ref, sys.modules[__name__] = sys.modules[__name__], MyModule('wat')

and it will work.

BTW, you don’t have to derive your class from types.ModuleType in order to put instances of it in sys.modules[]. Entries in sys.modules don’t have to be module objects (according to Alex Martelli).