使用切片交换索引？ [英] Swap indexes using slices?

问题描述

我知道你可以在Python中交换2个单个索引

I know that you can swap 2 single indexes in Python

r = ['1', '2', '3', '4', '5', '6', '7', '8'] 
r[2], r[4] = r[4], r[2]

输出：

['1', '2', '5', '4', '3', '6', '7', '8']

但是为什么你不能在python中交换2片索引？

But why can't you swap 2 slices of indexes in python?

r = ['1', '2', '3', '4', '5', '6', '7', '8'] 

我想将数字3 + 4与5 + 6 + 7换成r：

I want to swap the numbers 3 + 4 with 5 + 6 + 7 in r:

r[2:4], r[4:7] = r[4:7], r[2:4]

输出：

['1', '2', '5', '6', '3', '4', '7', '8']

预期产出：

['1', '2', '5', '6', '7', '3', '4', '8']

我错了什么？
输出：

What did I wrong? output:

推荐答案

切片工作正常。您正在更换不同长度的切片。 r [2：4] 是两项， r [4：7] 是三项。

The slicing is working as it should. You are replacing slices of different lengths. r[2:4] is two items, and r[4:7] is three items.

>>> r = ['1', '2', '3', '4', '5', '6', '7', '8']
>>> r[2:4]
['3', '4']
>>> r[4:7]
['5', '6', '7']

所以当 ['3'，'4'] 被替换时，它只能适合 ['5'，'6'] ，当 ['5'，'6'，'7'] 被替换时，它只获得 ['3' ，'4'] 。所以你有 ['1'，'2'，，然后接下来的两个元素是 ['5'，'6中的前两个元素'，'7'] 这只是 ['5'，'6'，然后来自的两个元素[ '3'，'4'接下来，然后剩下的'7'，'8'] 。

So when ['3', '4'] is replaced, it can only fit ['5', '6'], and when ['5', '6', '7'] is replaced, it only gets ['3', '4']. So you have ['1', '2',, then the next two elements are the first two elements from ['5', '6', '7'] which is just ['5', '6', then the two elements from ['3', '4' go next, then the remaining '7', '8'].

如果要替换切片，则必须在正确的位置开始切片，并为每个切片在数组中分配适当的大小：

If you want to replace the slices, you have to start slices at the right places and allocate an appropriate size in the array for each slice:

>>> r = ['1', '2', '3', '4', '5', '6', '7', '8']
>>> r[2:5], r[5:7] = r[4:7], r[2:4]
>>> r
['1', '2', '5', '6', '7', '3', '4', '8']
 old index: 4    5    6    2    3
 new index: 2    3    4    5    6

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