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

问题描述

我试图了解扩展在 Python 中的工作原理，但它并没有完全按照我的预期工作.例如:

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

但我会预料到:

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

为什么返回 None 而不是扩展列表?

解决方案

extend() 方法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 None 的返回值结束.

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
>>> 

But I would have expected:

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

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

解决方案

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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