Python:在遍历列表时编辑列表 [英] Python: Editing list while iterating over it

问题描述

Stack上有一些相关的问题，但我想尽可能清楚.我正在使用Python 3

There are some related questions on Stack but I wanted to be as clear as possible. I am using Python 3

如果我有一个列表，N，并且我使用以下代码:

If I have a list, N, and I use the following code:

N = [1,2,3,4,6,7,8]
for x in N:
    N[x] = N[x] * -1
return N

我得到一个Index out of range error.我知道您不应该在遍历列表时添加和删除元素，但是我想清楚地定义为什么上面的示例不起作用，对我来说似乎应该没有问题.在第一次迭代中，x应该计算为1.因此，如果我想编辑N[1]，我不明白为什么我无法编辑.

I am getting a Index out of range error. I understand you shouldn't be adding and deleting elements while iterating over a list, but I wanted a clear definition of why the above example won't work.To me, it seems like there shouldn't be a problem. In the first iteration, x should evaluate to 1. So if I want to edit N[1], I don't see why I wouldn't be able to.

作为旁注，我知道enumerate()是执行此操作的正确方法.

As a side note, I know enumerate() is the proper way to do it.

推荐答案

使用enumerate

例如:

N = [1,2,3,4,6,7,8]
for x, value in enumerate(N):
    N[x] = value * -1
print(N)

或列表理解.

例如:

N = [x * -1 for x in N]

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