I have a problem which requires a reversable 1:1 mapping of keys to values. That means sometimes I want to find the value given a key, but at other times I want to find the key given the value. Both keys and values are guaranteed unique. x = D[y] y == D.inverse[x] The obvious solution is to simply invert the dictionary every time I want a reverse-lookup: Inverting a dictionary is very easy, there's a recipe here but for a large dictionary it can be very slow. The other alternative is to make a new class which unites two dictionaries, one for each kind of lookup. That would most likely be fast but would use up twice as much memory as a single dict. So is there a better structure I can use? My application requires that this should be very fast and use as little as possible memory. The structure must be mutable, and it's strongly desirable that mutating the object should not cause it to be slower (e.g. to force a complete re-index) We can guarantee that either the key or the value (or both) will be an integer It's likely that the structure will be needed to store thousands or possibly millions of items. Keys & Valus are guaranteed to be unique, i.e. len(set(x)) == len(x) for for x in [D.keys(), D.valuies()] Continue reading...
