def add_metaclass(metaclass):
    """Class decorator for creating a class with a metaclass."""

    def wrapper(cls):
        orig_vars = cls.__dict__.copy()
        slots = orig_vars.get("__slots__")
        if slots is not None:
            if isinstance(slots, str):
                slots = [slots]
            for slots_var in slots:
                orig_vars.pop(slots_var)
        orig_vars.pop("__dict__", None)
        orig_vars.pop("__weakref__", None)
        if hasattr(cls, "__qualname__"):
            orig_vars["__qualname__"] = cls.__qualname__
        return metaclass(cls.__name__, cls.__bases__, orig_vars)

    return wrapper
Class decorator for creating a class with a metaclass.
lib/urllib3/packages/six.py