重複する要素を取り除く

>>> xs = [5, 8, 5, 1, 1, 4, 2, 4, 3, 2]
>>> set(xs)
set([1, 2, 3, 4, 5, 8])
>>> sorted(set(xs), key=xs.index) # 順序を維持
[5, 8, 1, 4, 2, 3]