class A:

    is_mutable = True

    def __init__(self, c):

        self.c = c

        self.is_mutable = False

    def __setattr__(self, name, value):

        if self.is_mutable:

            super().__setattr__(name, value)

        else:

            raise AttributeError("Immutable object")

    def __mul__(self, other):

        return self.__c + other.__c