def __init__(self):
    super(test, self).__init__({'a': 0, 'b': 1})

def keys(self):
    return ['a', 'b']

def __getitem__(self, item):
    return {'a': 0, 'b': 1}[item]

def __len__(self):
    return 2

def __contains__(self, item):
    pass
Construct a object which can be mapped or un packed