class A(object):
    def __init__(self, x):
        self.x = x

    def _get_y(self):
        return self.x * 2
    y = property(_get_y)

    def _get_z(self):
        return self.x * 2
    def __get_z(self):
        return self._get_z()
    z = property(__get_z)

class B(A):
    def _get_y(self):
        return self.x * 3
    #y = property(_get_y)
    def _get_z(self):
        return self.x * 3

a, b = A(1), B(1)
print(a.y, b.y)
print(a.z, b.z)
print(type(B.y))