unique-ifying a list

[Gabriel Genellina]

En Fri, 07 Aug 2009 17:53:10 -0300, kj <no.email at please.post> escribió:

> Suppose that x is some list.  To produce a version of the list with
> duplicate elements removed one could, I suppose, do this:
>
>     x = list(set(x))
>
> but I expect that this will not preserve the original order of
> elements.
>
> I suppose that I could write something like
>
> def uniquify(items):
>     seen = set()
>     ret = []
>     for i in items:
>         if not i in seen:
>             ret.append(i)
>             seen.add(i)
>     return ret

Assuming the elements are hashable, yes, that's the fastest way (minus
some microoptimizations like using local names for ret.append and
seen.add, or the 'not in' operator).

See bearophile's recipe [1], another one [2] by Tim Peters (quite old but
worths reading the comment section), and this thread [3]

[1] http://code.activestate.com/recipes/438599/
[2] http://code.activestate.com/recipes/52560/
[3] http://groups.google.com/group/comp.lang.python/t/40c6c455f4fd5154/

-- 
Gabriel Genellina