[已解决]求助

小向阳

为什么？

我的版本是python2.7，reverse（）不是倒序的吗？怎么会输出None？

最佳答案

月排行榜 / 总排行榜

donkkong

2017-3-4 22:07:22

>>> list1 = [1, 2, 3, 4, 5, 6, 7, 8]
>>> list1
[1, 2, 3, 4, 5, 6, 7, 8]
>>> list1.reverse()
>>> list1
[8, 7, 6, 5, 4, 3, 2, 1]
>>> list2 = list1
>>> list2
[8, 7, 6, 5, 4, 3, 2, 1]
>>> list3 = list2[-1::-1]
>>> list3
[1, 2, 3, 4, 5, 6, 7, 8]
>>>

跳转到最佳答案楼层

lubcat

1. >>> list1 = [1,2,3,4,5,6,7,8,9]
   
2. >>> list2 = list1.reverse()
   
3. >>> print(list2)
   
4. None
   
5. 
   
6. >>> type(list2)
   
7. <class 'NoneType'>
   
8. >>> type(list1.reverse())
   
9. <class 'NoneType'>
   
10. >>>

复制代码

零度非安全

s.reverse() reverses the items of s in place

Note:The sort() and reverse() methods modify the list in place for economy of space when sorting or reversing a large list. To remind you that they operate by side effect, they don’t return the sorted or reversed list.

donkkong

>>> list1 = [1, 2, 3, 4, 5, 6, 7, 8]
>>> list1
[1, 2, 3, 4, 5, 6, 7, 8]
>>> list1.reverse()
>>> list1
[8, 7, 6, 5, 4, 3, 2, 1]
>>> list2 = list1
>>> list2
[8, 7, 6, 5, 4, 3, 2, 1]
>>> list3 = list2[-1::-1]
>>> list3
[1, 2, 3, 4, 5, 6, 7, 8]
>>>

小向阳

lubcat 发表于 2017-3-4 21:16

谢谢啦

小向阳

donkkong 发表于 2017-3-4 22:07
>>> list1 = [1, 2, 3, 4, 5, 6, 7, 8]
>>> list1
[1, 2, 3, 4, 5, 6, 7, 8]

嗯嗯 会啦   谢谢啦

donkkong

不客气，加油