python之切片操作

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']

面对大河我无限惭愧

我年华虚度 空有一身疲倦

和所有以梦为马的诗人一样

岁月易逝 一滴不剩