class A(object):
    x:int = 1

    def get_A(self: "A") -> int:
        return self.x

class B(A):
    def __init__(self: "B"):
        pass

class C(B):
    z:bool = True

    def set_A(self: "C", val: int) -> object:
        self.x = val

a:A = None
b:B = None
c:C = None

a = A()
b = B()
c = C()

b.x = a.get_A()
a.x = b.get_A()
c.set_A(0)