TypeError: metaclass conflict

What it does

Checks for class definitions where the metaclass of the class being created would not be a subclass of the metaclasses of all the class's bases.

Why is it bad?

Such a class definition raises a TypeError at runtime.

Examples

class M1(type): ...
class M2(type): ...
class A(metaclass=M1): ...
class B(metaclass=M2): ...

# TypeError: metaclass conflict
class C(A, B): ...  # error