Python对List去重且不改变顺序

来源：https://www.cnblogs.com/wt11/p/7766042.html

mailto = ['cc', 'bbbb', 'afa', 'sss', 'bbbb', 'cc', 'shafa']
addr_to = list(set(mailto))
addr_to.sort(key = mailto.index)

结果一目了然

[1, 4, 3, 3, 4, 2, 3, 4, 5, 6, 1]
[1, 4, 3, 2, 5, 6]

如果不加sort语句的话则会变化顺序

[1, 4, 3, 3, 4, 2, 3, 4, 5, 6, 1]
[1, 2, 3, 4, 5, 6]