Python ABC / Virtual Subclasses

from abc import ABC, abstractmethod


class A(ABC):
    def __init__(self):
        self.a = 0
        pass

    @abstractmethod
    def hello(self):
        pass

    @classmethod
    def __subclasshook__(cls, K):
        if K is tuple:
            return True
        return NotImplemented


class B(A):
    def __init__(self):
        super().__init__()

    def hello(self):
        print('B hello')


class C(B):
    def __init__(self):
        super().__init__()

    def hello(self):
        print('C hello')

    def chk(self):
        for c in C.__mro__:
            print(c)

    def __getitem__(self, item):
        if item >= 3:
            raise IndexError('index out of range: {}'.format(item))
        return item

    def __len__(self):
        return 3


def main():
    t = 1, 2, 3
    c = C()
    c.hello()
    c.chk()

    # these are ok
    print(isinstance(c, A))
    print(isinstance(c, B))
    print(isinstance(c, C))

    # what's the use??
    print(issubclass(tuple, A))


if __name__ == '__main__':
    main()