Python: find all classes which inherit from this one? [duplicate]

You want to use Widget.__subclasses__() to get a list of all the subclasses. It only looks for direct subclasses though so if you want all of them you’ll have to do a bit more work:

def inheritors(klass):
    subclasses = set()
    work = [klass]
    while work:
        parent = work.pop()
        for child in parent.__subclasses__():
            if child not in subclasses:
                subclasses.add(child)
                work.append(child)
    return subclasses

N.B. If you are using Python 2.x this only works for new-style classes.