types.py 文件源码

def generate_immutable_abc(supercls, mutable_subclass):

    class ABCImmutableMeta(ABCMeta):

        def __subclasscheck__(cls, subclass):
            if not issubclass(subclass, supercls):
                return False
            return not issubclass(subclass, mutable_subclass)

    class ABCImmutable(with_metaclass(ABCImmutableMeta, object)):
        pass

    # dirty hack to assert issubclass(ABCImmutable, supercls).
    supercls._abc_cache.add(ABCImmutable)

    return ABCImmutable