Merge metaclasses ad-hoc to solve metaclass conflicts

mergemetaclasses.py

from typing import Type, Optional


def merge_metaclasses(*bases: Type, metaclass: Optional[Type] = None) -> Type:
    """
    Make an ad-hoc metaclass to resolve conflicts in class declarations.

    Makes a metaclass that inherits from all of the metaclasses involved in a class
    declaration: the metaclasses of the bases and the explicit metaclass. The
    inheritance order is the explicit metaclass first and then the bases'
    metaclasses, in order.
    """
    metaclasses = []
    if metaclass is not None:
        metaclasses.append(metaclass)
    for cls in bases:
        mcs = type(cls)
        if mcs not in metaclasses:
            metaclasses.append(mcs)

    name = "_".join(mcs.__name__ for mcs in metaclasses)
    return type(name, tuple(metaclasses), {})