Does turning a list into a set, then back again, cause problems in Python?

Question

I'm turning a list into a set in Python, like so:

request.session['vote_set'] = set(request.session['vote_set'])

So I can easily do a if x in set lookup and eliminate duplicates. Then, when I'm done, I reconvert it:

request.session['vote_set'] = list(request.session['vote_set'])

Is there a better way to do this? Am I potentially doing something dangerous (or stupid)?

Answer 1

You'll lose ordering, if that's important to you.

Answer 2

You'll lose duplicates if you actually wanted them. If this is actually a list of "votes" as your naming suggests, you'd 'lose' some :)

why not just:

if x in set(request.session['vote_set'])

if you're worried.

Although I have to wonder if that would be slower than just plain:

if x in request.session['vote_set']

And ordering, as others have mentioned, would potentially (most likely) be lost.

Answer 3

This is how you remove duplicates AND maintain the order (if you care): http://stackoverflow.com/questions/1801459/algorithm-how-to-delete-duplicate-elements-in-a-list-efficiently

The other answers showed how to turn a list into a set.