To modify a class, use composite pattern instead of inheriting a base class

composite_pattern_modifying_another_class.py

class BaseClass:
    def __init__(self, _id, a, k=None):
        self.id = _id
        self.a = a
        self.k = k

    def updated(self, **kwargs):
        kwargs = {"k": self.k, **kwargs}
        return BaseClass(self.id, self.a, **kwargs)

    def say_it(self):
        self.k *= -1
        print(f"hello! {self.k}")

    def __repr__(self):
        return f"BaseClass({self.id}, {self.a}, k={self.k})"


class ModifiedClass:
    def __init__(self, *args, **kwargs):
        assert len(args) == 1
        self._BaseClass = BaseClass(None, *args, **kwargs)

    def __getattr__(self, name):
        if name == "id":
            raise AttributeError("a ModifiedClass is not identifiable")
        try:
            return getattr(self._BaseClass, name)
        except AttributeError:
            pass
        raise AttributeError(f"'ModifiedClass' object has no attribute '{name}'")

    def updated(self, **kwargs):
        return self.from_BaseClass(self._BaseClass, **kwargs)

    def __repr__(self):
        return f"ModifiedClass({self.a}, k={self.k})"

    @staticmethod
    def from_BaseClass(BaseClass: BaseClass, **kwargs):
        kwargs = {"k": BaseClass.k, **kwargs}
        return ModifiedClass(BaseClass.a, **kwargs)


d = BaseClass(3, 4, k=5)
u = d.updated(k=6)
print(d)
print(u)
print(u.a, u.k, u.id)
print(isinstance(u, BaseClass))
u.say_it()

print()

t = ModifiedClass(4, k=5)
u = t.updated(k=6)
print(t)
print(u)
print(u.a, u.k, u._BaseClass)
print(isinstance(u, BaseClass))
u.say_it()
u.say_it()
# u.z