Python函数正在更改输入的值，但我不知道为什么 [英] Python function is changing the value of my input, and I can't figure out why

问题描述

这是我的第一个问题，因此，如果我正在发布此消息，请让我知道为什么以及将来如何避免它！

This is my first question, so if I'm being a total dweeb posting this, let me know why and how I can avoid it in the future!

我有一些python代码，应该只列出一个列表，并将第j个组件乘以-1.这是有问题的代码.

I have a bit of python code that should just take a list, and multiply the jth component by -1. This is the code in question.

def flip(spins,j):
    z = spins
    z[j] = z[j]*-1
    return z

但是，我要注意的是，如果我尝试做类似的事情

However, what I am noticing is that if I try to do something like

spin = [1,1,1]
test = flip(spin,1)

它将为[test]分配适当的值[1，-1,1]，但还将'spin'的值更改为[1，-1,1].我知道有些东西完全可以忽略，但是我一直盯着它看了2个小时，仍然看不到它.

it will assign the proper value [1,-1,1] to 'test', but it will also change the value of 'spin' to [1,-1,1]. I know there must be something totally obvious I'm overlooking, but I've been staring at this for 2 hours and still can't see it.

感谢您的帮助！

推荐答案

在函数中，z和spins引用相同的列表，也称为spin的全局名称.如果您修改其中一个，则这些更改也可以通过其他名称看到.变量z是多余的.

Inside your function, z and spins refer to the same list, which is also known by the global name of spin. If you modify one, those changes are visible through the other names as well. The variable z is superfluous.

如果您希望z是spins的副本，则只需执行以下操作:

If you want z to be a copy of spins then just do:

z = spins[:]

或:

z = list(spins)

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