from abc import ABCMeta

class Animal(metaclass=ABCMeta):
    pass

class Plant(metaclass=ABCMeta):
    def __init_subclass__(cls):
        global broken_class
        broken_class = cls
        assert not issubclass(cls, Animal), "Plants cannot be Animals"

class Dog(Animal):
    pass

try:
    class Triffid(Animal, Plant):
        pass
except Exception as e:
    pass

# prints True, that's probably bad
print(broken_class in Animal.__subclasses__())

# Animal is properly initialized, therefore this is True
print("_abc_impl" in Animal.__dict__)
# since Triffid wasn't properly initialized, it's also missing an _abc_impl attribute
print("_abc_impl" in broken_class.__dict__)
# therefore if you read that attribute, it is found via its base class Animal
print(broken_class._abc_impl is Animal._abc_impl)