切片

切片：访问特定范围的元素,提取序列的一部分。使用两个索引，中间用：，还可以指定步长（默认为1）,[[start]:[stop]:[step]]b

>>> numbers = list(range(0,11))
>>> numbers[0:5]
[0, 1, 2, 3, 4]
>>> numbers[:5]
[0, 1, 2, 3, 4]
>>> numbers[5:]
[5, 6, 7, 8, 9, 10]
>>> numbers[:]
[0, 1, 2, 3, 4, 5, 6, 7, 8, 9, 10]
>>> numbers[-3:]
[8, 9, 10]
>>> numbers[-3:-1]
[8, 9]
>>> numbers[-3:0]
[]
>>> numbers[0:10:2]
[0, 2, 4, 6, 8]
>>> numbers[3:10:4]
[3, 7]
>>> numbers[8:3:-1]
[8, 7, 6, 5, 4]
>>> numbers[0:10:-2]
[]
>>> numbers[5::-2]
[5, 3, 1]
>>> numbers[:5:-2]
[10, 8, 6]

note：1：切片可以用来复制序列，相当于浅复制
           2：遍历切片可以使用for循环。
 

>>> numbers = list(range(0,11))
>>> numbers1 = numbers[:]
>>> numbers1[0] = 'a'
>>> print(numbers,numbers1,sep = '\n')
[0, 1, 2, 3, 4, 5, 6, 7, 8, 9, 10]
['a', 1, 2, 3, 4, 5, 6, 7, 8, 9, 10]
>>> for value in numbers1:
...     print(value)
...
a
1
2
3
4
5
6
7
8
9
10
>>>