Sometimes dictionaries are better than lists.
I had a huge list of numbers, and I was generating new numbers which I needed to check for membership in the list. So, I was doing lots of
item in list. However this proved to be very slow. So slow that the program would have run for several days before completing.
So, I stuck all of the list items in a dictionary and did
dictionary.has_key(item). The program ran in about a second.
Lesson: Use the right tool for the job.