在Python中使用列表进行扩展的意外行为 [英] Unexpected Behavior of Extend with a list in Python

问题描述

我试图了解扩展在Python中的工作方式，但并没有达到我的期望.例如:

I am trying to understand how extend works in Python and it is not quite doing what I would expect. For instance:

>>> a = [1, 2, 3]
>>> b = [4, 5, 6].extend(a)
>>> b
>>> 

但我本来期望:

[4, 5, 6, 1, 2, 3]

为什么返回None而不是扩展列表?

Why is that returning a None instead of extending the list?

推荐答案

extend()方法将追加到现有数组并返回None.在您的情况下，您正在动态创建一个数组-[4, 5, 6]-对其进行扩展，然后将其丢弃.变量b以返回值None结尾.

The extend() method appends to the existing array and returns None. In your case, you are creating an array — [4, 5, 6] — on the fly, extending it and then discarding it. The variable b ends up with the return value of None.

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