def METHOD_NAME(cls, membername, initfunc, **kwargs):
    'Overload Extensible.init() to call finalInit instead of __init__'
    oldinit = cls.finalInit
    def newinit(self, *args, **kwargs):
        oldinit(self, *args, **kwargs)
        setattr(self, membername, initfunc())
    cls.finalInit = newinit
    super().METHOD_NAME(membername, lambda: None, **kwargs)