How to properly decorate a function to be overridden in python?

Question

I'd like to designate some of my baseclass functions for override. (The override should not be necessarily enforced.) What is the proper way of doing this?

I mean sth like

class Base(object):
    ...
    @abstractmethod
    def fun(self):
        pass

class Derived(Base):

    @override
    def fun(self):
        pass

EDIT:

I want my code to raise an UnimplementedException if the function is not overridden.

Answer 1

class Base(object):
    ...
    def fun(self):
        raise NotImplementedError

Source: http://julien.danjou.info/blog/2013/guide-python-static-class-abstract-methods