Can a base class know if a method has been overridden?

[Ratko]

> If your use case is to make sure a given ('abstract') method has been
> overriden, the canonical solution is to raise NotImplementedError in the
> base class's implementation

I am not really interested in forcing the subclass to implement a
method. I am interested in knowing *whether* it did implement it or
not.


> Else, this may be possible using a custom metaclass (or possibly just
> specializing the __new__ method), but there may be better solutions
> (depending on what you're really trying to do)..

I have a base class EvtHandler that has methods defined to handle
certain events. You then subclass from EvtHandler and override the
methods for the events you want to receive. If a method has been
overridden, the base class will automatically register for those
events to make sure that they are even delivered to this handler
(which is why I would need to know whether a method has been
overridden or not). Of course, there are other ways of doing this
which would require a bit more work from the subclass... I just
thought this would be a neat "automatic" way of registering for
events.

For example:

class EvtHandler:
    def __init__(self):
        if onKey is overridden:
             register_for_key_events()

    def onKey(self):
        pass


class MyHandler(EvtHandler):
    def onKey(self):
        # do something here....