weird-metaclass-stuff.py

# Python 3.3 only


class klass(object):
    def __init__(self, name, klass, bases, children=None):
        self.name = name
        self.klass = klass
        self.bases = bases
        self.children = children or []

    def __repr__(self):
        return '{} {}({})'.format(self.klass, self.name,
                                  [b.__name__ for b in self.bases])


class SubClassTracker(type):
    tracker = {}

    def __new__(cls, name, base_classes, attrs):
        SubClassTracker.tracker[name] = klass(name, cls, base_classes)
        for b in base_classes:
            bname = b.__name__
            if bname in SubClassTracker.tracker:
                SubClassTracker.tracker[bname].children.append(name)

        return type.__new__(cls, name, base_classes, attrs)


class ParentClass(metaclass=SubClassTracker):
    def __init__(self, foo):
        self.foo = foo

    def __repr__(self):
        return 'ParentClass(foo={})'.format(self.foo)


class ChildClass(ParentClass):
    def __init__(self, foo, bar):
        super(ChildClass, self).__init__(foo)
        self.bar = bar

    def __repr__(self):
        return 'ChildClass(foo={}, bar={})'.format(self.foo, self.bar)


class ChildClass2(ParentClass):
    def __init__(self):
        super(ChildClass2, self).__init__(True)

    def __repr__(self):
        return 'ChildClass2()'


def InbredGrandchildClass(ChildClass, ChildClass2):
    def __init__(self):
        self.bar = 1


c = ChildClass(1, 2)