在列表的元素中添加空格 [英] Add spaces to elements of list

问题描述

我已经为此苦苦挣扎了一段时间.我有一个带有子列表的列表，我想在子列表的每个元素之前添加一个空格.例如:

I've been struggling for a while with this. I have a list with sublist and I wanted to add an element that is a space before each element of the sublists. for example:

lin = [[2], [3], [2], [2, 2], [2]]

结果应该是:

lin = [[' ',2], [' ',3], [' ',2], [' ',2, ' ',2], [' ',2]]

我试图做到这一点:

for a in lin:
    for e in a:
        e = (' ') , e 

但是我获得了完全相同的列表，没有任何改动

but I obtained exactly the same list with no alterations

推荐答案

我认为您实际上的意思是类似Tigerhawk的评论.

I assume that you actually meant something like the comment of Tigerhawk.

您的问题是e= (' ') , e只是将e的值(原来是嵌套列表中的每个值)覆盖为包含空格和原始值的元组.这实际上并不会更改列表中的任何内容，只会更改e最初指向的内容.

Your problem is that e= (' ') , e is just overwriting the value of e (which was originally each value in your nested list) to a tuple containing a space and the original value. This doesnt actually change anything inside of your list, just changes whatever it is that e was originally pointing to.

您可以改为执行以下操作:

You can instead do something like this:

>>> lin = [[2], [3], [2], [2, 2], [2]]
>>> for a in lin:
        for i in range(len(a)-1,-1,-1):
            a.insert(i, ' ')


>>> lin
[[' ', 2], [' ', 3], [' ', 2], [' ', 2, ' ', 2], [' ', 2]]

请注意内部循环:for i in range(len(a)-1,-1,-1):之所以这样做是出于两个原因:

Note the inner loop: for i in range(len(a)-1,-1,-1): This is done this way because of 2 reasons:

1. 您不想实际遍历a，因为您将要更改a中的值
2. 您需要从最高索引开始，因为如果从0开始，则其前面其余项目的索引将发生变化.

1. you dont want to be actually looping through a since you are going to be changin the values in a
2. You need to start with the highest index because if you start from 0, the indexes of the rest of the items ahead of it will change.

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