无法在循环中修改列表元素 [英] Can't modify list elements in a loop

问题描述

在Python中遍历列表时，如果没有列表理解，我将无法修改元素.供参考:

While looping over a list in Python, I was unable to modify the elements without a list comprehension. For reference:

li = ["spam", "eggs"]
for i in li:
    i = "foo"

li
["spam", "eggs"]

li = ["foo" for i in li]
li 
["foo", "foo"]

那么，为什么我不能通过Python中的循环来修改元素?肯定有一些我想念的东西，但是我不知道是什么.我确定这是重复的，但是我找不到与此相关的问题，如果有链接，那就绰绰有余了.

So, why can't I modify elements through a loop in Python? There's definitely something I'm missing, but I don't know what. I'm sure this is a duplicate, but I couldn't find a question about this, and if there is a link, that would be more than enough.

推荐答案

因为 i in li 的工作方式如下:

for idx in range(len(li)):
    i = li[idx]
    i = 'foo'

因此，如果您为 i 分配任何内容，则不会影响 li [idx] .

So if you assign anything to i, it won't affect li[idx].

解决方案要么是您提出的，要么是遍历索引:

The solution is either what you have proposed, or looping through the indices:

for idx in range(len(li)):
    li[idx] = 'foo'

或使用枚举:

for idx, item in enumerate(li):
    li[idx] = 'foo'

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