Set data structure..

[Alessio Pace]

Hi, I am a python newbie, so this could be a silly question:
I need a Set like data structure, I just see list and dictionary as
built-in. Should I use one of those for my set purpose(I was thinking about
using a dictionary giving meaning only to the keys, but it seems a waste of
space for large inputs) and if so, which one has better access performance
to check if an element is in the set? Thanks!