class A:
    def __init__(self, factor):
        self.__factor = factor

    def op1(self):
        print('Op1 with factor {}...'.format(self.__factor))

class B(A):
    def op2(self, factor):
        self.__factor = factor
        print('Op2 with factor {}...'.format(self.__factor))

obj = B(1000)
obj.op1()
obj.op2(42)
obj.op1()