subclass __module__ set to metaclass module when manually creating new class with type()

Question

In the following example, the newly created subclass ends up being the metaclass __module__ rather than the parent classes\' module. I\'ve only seen this happe

Answer 1

If no __module__ key is present in the mapping passed to type.__new__, type.__new__ determines __module__ based on the module where the call to type.__new__ occurs, by looking for __name__ in the globals of the top Python stack frame.

When you run newclass = type('newclass', (test,), {}), the type constructor delegates to abc.ABCMeta, which then calls type.__new__ from inside the abc module, so type thinks that __module__ should probably be abc.

When you write the class statement

class subtest(test):
    pass

The compiled bytecode for the class statement automatically includes a __module__ = __name__ assignment, which uses the current module's __name__ instead of abc.__name__.

If you want to control the value of __module__ for a class created by calling type directly, you can set the key in the original mapping, or assign to the class's __module__ after creation:

newclass = type('newclass', (test,), {'__module__': __name__})

# or

newclass = type('newclass', (test,), {})
newclass.__module__ = __name__