def put_unique(self, _id, key=None, value=None, **pair):
        return self.update(_id, key, value, **pair)

    # TODO: maybe a putIfAbsent method too
Put an element into the index at key/value and overwrite it if an 
dataset/ETHPy150Open espeed/bulbs/bulbs/neo4jserver/index.py/Index.put_unique