使用列表推導，只保留元素個數等於1的

a = ["a", "b", "c", "d", "a", "a"]b = [x for x in a if a.count(x) == 1]print b

列表推導中的x for x in a if a.count(1) == 1和下面的for迴圈等價，不過更簡潔：

b = []for x in a: if a.count(x) == 1: b.append(x)print b

程式碼如下：

oldList = ["a","b","c","d","a","a"]

newList = []

for letter in oldList:

if letter not in newList:

newList.append(letter)

print newList

執行結果：

["a", "b", "c", "d"]