Lec4 Slice

Slice ： list切片操作符

 

L[0:3]表示从索引0开始取到索引3但不包括3，即索引0，1，2。

>>> L = ['lr','hjr','hjj','lqq']
>>> L[0:3]
['lr', 'hjr', 'hjj']

 

若第一个索引为0可以省略：

>>> L[:3]
['lr', 'hjr', 'hjj']

 

L[:]取所有：

>>> L[:]
['lr', 'hjr', 'hjj', 'lqq']

 

倒数切片：L[-1]取倒数第一个元素， L[-2:]表示从倒数第2个开始取到最后：

>>> L[-2:]
['hjj', 'lqq']

 

例子：先创建数列0～99  range（100）

>>> L=list(range(100))
>>> L
[0, 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 16, 17, 18, 19, 20, 21, 22, 23, 24, 25, 26, 27, 28, 29, 30, 31, 32, 33, 34, 35, 36, 37, 38, 39, 40, 41, 42, 43, 44, 45, 46, 47, 48, 49, 50, 51, 52, 53, 54, 55, 56, 57, 58, 59, 60, 61, 62, 63, 64, 65, 66, 67, 68, 69, 70, 71, 72, 73, 74, 75, 76, 77, 78, 79, 80, 81, 82, 83, 84, 85, 86, 87, 88, 89, 90, 91, 92, 93, 94, 95, 96, 97, 98, 99]

1.前10位

>>> L[:10]
[0, 1, 2, 3, 4, 5, 6, 7, 8, 9]

2.后10位

>>> L[-10:]
[90, 91, 92, 93, 94, 95, 96, 97, 98, 99]

3.第10～20位

>>> L[9:19]
[9, 10, 11, 12, 13, 14, 15, 16, 17, 18]

4.前10位每两个取一个

>>> L[:10:2]
[0, 2, 4, 6, 8]

5.所有数每5个取一个

>>> L[::5]
[0, 5, 10, 15, 20, 25, 30, 35, 40, 45, 50, 55, 60, 65, 70, 75, 80, 85, 90, 95]

6.用slice复制list

>>> L[:]
[0, 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 16, 17, 18, 19, 20, 21, 22, 23, 24, 25, 26, 27, 28, 29, 30, 31, 32, 33, 34, 35, 36, 37, 38, 39, 40, 41, 42, 43, 44, 45, 46, 47, 48, 49, 50, 51, 52, 53, 54, 55, 56, 57, 58, 59, 60, 61, 62, 63, 64, 65, 66, 67, 68, 69, 70, 71, 72, 73, 74, 75, 76, 77, 78, 79, 80, 81, 82, 83, 84, 85, 86, 87, 88, 89, 90, 91, 92, 93, 94, 95, 96, 97, 98, 99]

 

tulpe进行切片操作结果还是tuple：

>>> t = (1,2,3,4,5)
>>> t[:3]
(1, 2, 3)

str进行切片操作结果仍为str：

>>> "ABCDEF"[:4]
'ABCD'