Python - 直接扩展列表会导致 None，为什么?
x=[1,2,3]
x.extend('a')
输出:
x is [1,2,3,'a']
但是当我执行以下操作时:
But when I do the following:
[1,2,3].extend('a')
输出:
None
为什么扩展对列表引用有效，而对列表无效?
Why does extend work on a list reference, but not on a list?
我发现这个是因为我试图将 listB 附加到 listA，同时尝试将 listC 扩展到 listB.
I found this because I was trying to append a listB to a listA while trying to extend listC to listB.
listA.append([listB[15:18].extend(listC[3:12])])
假设列表不能直接附加/扩展.解决此问题最流行的变通方法是什么?
Supposing lists cannot be directly appended / extending. What is the most popular work around form for resolving this issue?
list.extend 就地修改列表并且不返回任何内容，从而导致 None.在第二种情况下，它是一个正在扩展的临时列表，该列表在该行之后立即消失，而在第一种情况下，它可以通过 x 引用.
list.extend modifies the list in place and returns nothing, thus resulting in None. In the second case, it's a temporary list that is being extended which disappears immediately after that line, while in the first case it can be referenced via x.
在尝试将 listC 扩展到 listB 时将 listB 附加到 listA.
to append a listB to a listA while trying to extend listC to listB.
不要使用 extend，你可能想试试这个:
Instead of using extend, you might want to try this:
listA.append(listB[15:18] + listC[3:12])
如果您想实际修改listB 或listCcode>，或者使用extend 以多行简单的方式进行.
Or do it in multiple simple lines with extend if you want to actually modify listB or listC.