class Lazy(type):
    def __init__(cls, name, bases, dict):
        super(Lazy, cls).__init__(name, bases, dict)
        cls.instance = None

    def check_instance(cls):
        if cls.instance is None:
            if hasattr(cls, 'instantiate'):
                setattr(cls, 'instance', getattr(cls, 'instantiate')())
            else:
                raise Exception('Must implement the instantiate class method!')

    def __getattr__(cls, name):
        cls.check_instance()
        return getattr(cls.instance, name)

    def __getitem__(cls, key):
        cls.check_instance()
        return cls.instance.__getitem__(name)

    def __iter__(cls):
        cls.check_instance()
        return cls.__iter__()

    def __contains__(self, item):
        cls.check_instance()
        return cls.__contains__(item)