python列表类型extend()与append()
append() 只追加得到额外的一个元素,可以认为是tuple，extend()只能是一个列表
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>>> a=[1,2]
>>> b=[3,5]
>>> c=[3,5]
>>> b.append(a)
>>> c.extend(a)
>>> b
[3, 5, [1, 2]]
>>> c
[3, 5, 1, 2]
>>> len(b)
3
>>> len(c)
4
set 无序不重复元素集
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>>> a = [5, 2, 5, 1, 4, 3, 4]
>>> print a
[5, 2, 5, 1, 4, 3, 4]
>>> print set(a)
set([1, 2, 3, 4, 5])
>>>
set list互转
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>>> a=set('123456')
>>> a
set(['1', '3', '2', '5', '4', '6'])
>>> b=list(a)
>>> b
['1', '3', '2', '5', '4', '6']
>>> s=set(b)
>>> s
set(['1', '3', '2', '5', '4', '6'])