bi_dict.py

class BiDict(object):
    '''
    Maps both directions: key->value and value->key

    Requires both keys and values are unique. If you pass duplication,
    then key/value be overwritten and you get not what expected.
    '''
    origin = {}  # counters the {key->key} case
    bidict = {}

    def __init__(self, **kwargs):
        for key, value in kwargs.items():
            self.origin[key] = value
            self.bidict[key] = value
            self.bidict[value] = key

    def __getitem__(self, key):
        return self.bidict[key]

    def __setitem__(self, key, value):
        # Remove any previous connections with these values
        if key in self.origin:
            self.__delitem__(key)
        if value in self.origin:
            self.__delitem__(value)
        self.origin[key] = value
        self.bidict[key] = value
        self.bidict[value] = key

    def __delitem__(self, key):
        del self.bidict[key]
        del self.bidict[self.origin[key]]
        del self.origin[key]

    def __len__(self):
        return len(self.origin)

    def __iter__(self):
        return self.origin.__iter__()

    def items(self):
        return self.origin.items()

    def keys(self):
        return self.origin.keys()

    def values(self):
        return self.origin.values()