Generic metaclass to keep track of subclasses?

Question

I\'m trying to write a generic metaclass to track subclasses

Since I want this to be generic, I didn\'t want to hardcode any class name within this metaclass, therefore

Answer 1

I think you want something like this (untested):

class SubclassTracker(type):
    def __init__(cls, name, bases, dct):
        if not hasattr(cls, '_registry'):
            cls._registry = []
        print('registering %s' % (name,))
        cls._registry.append(cls)
        super(SubclassTracker, cls).__init__(name, bases, dct)

Then, for Python 2, you can invoke it like:

class Root(object):
    __metaclass__ = SubclassTracker

for Python 3

class Root(object, metaclass=SubclassTracker):

Note that you don't need to stick the _registry attribute on there because stuff like that is what metaclasses are for. Since you already happen to have one laying around... ;)

Note also that you might want to move the registration code into an else clause so that the class doesn't register itself as a subclass.