l = ['c', 'a', 't', 'd', 'o', 'g', 'r', 'a', ...[c for i, c in enumerate(l) if c not in l[:i]]或 [c for c in set(l)],不過 set 不保證順序,若要順序一致可以參考 OrderedSet
http://bit.ly/1C7ns1Ot = []; [c for w in l for c in w if c not in t \and t.extend(c)]上面這行是當 l = ['cat', 'dog', 'rabbit'] 時。