python之切片操作

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字符串、列表、元组（tuple）在python中都符合“序列”这一特征，符合“序列”特征的对象都可以使用切片（slice）去访问它们的任意部分，切片操作符在python中的原型是：

[start:stop:step]，表示为[开始索引:结束索引:步长]

开始索引：从0开始，序列从左向右累增计数，最一个值的索引记为-1；
结束索引：切片操作到此为止，不包含该索引的值；
步长：步长表示切片的间隔，默认步长为1，如果步长为负数，则表示从右向左取，步长不能为0；

常规切片操作

>>> L = ['A','B','C','D','E']>>> L[::]['A','B','C','D','E']>>> L[0:-1:1]['A','B','C','D']>>> L[0:5]['A','B','C','D','E']>>> L[::2]['A','C','E']>>> L[0:100:2]['A','C','E']>>> L[::-1]['E','D','C','B','A']>>> L[4:0:-1]['E','D','C','B']>>> L[:]['A','B','C','D','E']>>> L[-3:-1]['C','D']>>> L[-3:]['C','D','E']

使用切片操作对列表插入和修改元素

>>> L = ['A','B','C','D','E']>>> L[2:0] = ['F']['A','B','F','C','D','E']>>> L = ['A','B','C','D','E']>>> L[2:1]=['F']['A','B','F','C','D','E']>>> L = ['A','B','C','D','E']>>> L[2:2]=['F']['A','B','F','C','D','E']>>> L = ['A','B','C','D','E']>>> L[2:3]=['F']['A','B','F','D','E']>>> L = ['A','B','C','D','E']>>> L[2:4]=['F']['A','B','F','E']>>> L = ['A','B','C','D','E']>>> L[2:5]=['F']['A','B','F']

删除切片

>>> L = ['A','B','C','D','E']>>> del L[2:2]['A','B','C','D','E']>>> L = ['A','B','C','D','E']>>> del L[2:3]['A','B','D','E']>>> L = ['A','B','C','D','E']>>> del L[2:-1]['A','B','E']>>> L = ['A','B','C','D','E']>>> del L[2:]['A','B']

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