How do I check if a method was overwritten by a child class?

Question

I want to be able to check if a child class has overwritten a method. For example,

class Foo:
    def __init__(self):
        # Is there something following this sort of spec?
        print("overridden" if self.bar != Foo.bar else "not overridden")
    def bar(self):
        return 0

An inherited method that overwrites bar might be:

class Kung(Foo):
    def __init__(self):
        super(Kung, self).__init__()
    def bar(self):
        return 1

In this case, Kung() should print "overridden", but Foo() should print "not overridden". Can I check whether bar was overwritten in the __init__ of Foo without checking the return value?

Answer 1

This is a very strange thing to do. I question the design that would require this. In any case, you could check something like:

class Foo:
    def __init__(self):
        try:
            bar = type(self).bar
        except AttributeError:
            bar = None
        if bar is None or bar is Foo.bar:
            print("not overriden")
        else:
            print("overridden")

    def bar(self): return 0

This works because you are checking for bar on the class objects. If you use some_instance.some_method then that creates a new method object on each invocation, which is why your approach won't work.

Consider:

>>> class Foo:
...     def bar(self): pass
...
>>> foo = Foo()
>>> foo.bar is foo.bar
False

However,

>>> Foo.bar is Foo.bar
True