python: delete the duplicates in a list

下面有几种做法,  其中3之简洁令人惊讶. 

1, 

>>> t = [1, 2, 3, 1, 2, 5, 6, 7, 8]
>>> t
[1, 2, 3, 1, 2, 5, 6, 7, 8]
>>> list(set(t))
[1, 2, 3, 5, 6, 7, 8]
>>> s = [1, 2, 3]
>>> list(set(t) - set(s))
[8, 5, 6, 7]

 2, 

def f7(seq):
    seen = set()
    seen_add = seen.add
    return [x for x in seq if not (x in seen or seen_add(x))]

 3, 

myList = sorted(set(myList))

 4, 

for i in mylist:
  if i not in newlist:
    newlist.append(i)