list, set操作

def union_list(l1, l2):
    result = []
    if not l1:
        result.extend(l2)
        return result
    if not l2:
        result.extend(l1)
        return result
    result.extend(l1)
    for i in set(l1+l2):
        if i not in l1:
            result.append(i)
    return result

set(l1+l2) 也可以达到以上目的，但是会重新排序。上述程序保留l1的顺序。

set 的操作：

联合（Union） 交集（Intersection） 差集（Difference）

a | b  # union

a & b # intersection

a ^ b # in a or in b but not in a & b   equals   a.symmetric_difference(b)

set的减法与被减数相关，等同set.difference(): all elements that are in this set but not the others.

>>m = set('arwb+tU')
>>m
set(['a', 'b', '+', 'r', 'U', 't', 'w'])
>>set('r') - m
set([])  # False
>> set('2') - m
set([2])  # True

>>l = [1, 2, 3]
>>ll = [2, 4, 6]
>> set(l) - set(ll)
set([2])

>> ll = [4, 6]
>> set(l) - set(ll)
set([1, 2, 3])

去掉 list 中的重复元素：

{}.fromkeys(list).keys()
or
set(list)

遍历

for i in alist:
    print i

for index, item in enumerate(alist):
    print index, item

 list 加法

alist = [2, 3]
s = ["dfjo"]+alist  
>>s
['dfjo', 2, 3]