Python static method and class inheritance

class Base(object):

    _MY_VALUE = None

    @classmethod
    def my_value(cls, value=None):
        if value:
            cls._MY_VALUE = value
        return cls._MY_VALUE


class Child1(Base):

    pass


class Child2(Base):

    pass


if __name__ == '__main__':
    print Child1.my_value()
    print Child1.my_value(value=1)
    print Child1.my_value()
    print Child1().my_value()
    print Child2.my_value()
    print Child2().my_value()
    print Base.my_value()

None
1
1
1
None
None
None