How do I dynamically add mixins as base classes without getting MRO errors?

Question

Say I have a class A, B and C.

Class A and B are both mixin classes for Class C.

Answer 1

Think of it this way -- you want the mixins to override some of the behaviors of object, so they need to be before object in the method resolution order.

So you need to change the order of the bases:

class C(A, B, object):
    pass

Due to this bug, you need C not to inherit from object directly to be able to correctly assign to __bases__, and the factory really could just be a function:

class FakeBase(object):
    pass

class C(FakeBase):
    pass

def c_factory():
    for base in (A, B):
        if base not in C.__bases__:
            C.__bases__ = (base,) + C.__bases__
    return C()