A data-structure for 1:1 mappings in python?

Question

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

Answer 1

The other alternative is to make a new class which unites two dictionaries, one for each > kind of lookup. That would most likely use up twice as much memory as a single dict.

Not really, since they would just be holding two references to the same data. In my mind, this is not a bad solution.

Have you considered an in-memory database lookup? I am not sure how it will compare in speed, but lookups in relational databases can be very fast.