为什么修改数组副本会影响原始副本? [英] Why does modifying copy of array affect original?

问题描述

大家好，如果这是一个菜鸟问题，我很抱歉，但是我使用的是python，但是我在复制数组时遇到问题，但是当我修改副本时，它会影响原始数组.我想将边界矩阵的线性偏移量添加到一组坐标:

Hi everyone I am sorry if this is a noob question but I am using python and I have an issue where I copy an array but then when I modify the copy it affects the original. I want to add a linear offset from the boundaries matrix to a set of coordinates:

boundaries = [[5.818, 0.0, 0.0], [0.0, 5.818, 0.0], [0.0, 0.0, 5.818]]

xyzCoord = [[0.0, 0.0, 0.0], [2.909, 2.909, 0.0], ...

extraX=[]
for i in range(0,len(xyzCoord)):
    toAdd=[]
    toAdd=xyzCoord[i]
    toAdd[0]=toAdd[0]+boundaries[0][0]

print xyzCoord

我期望的输出是xyzCoord不会受到影响，因为我进行了复制(toAdd)，然后对其进行了修改.奇怪的是，此循环确实影响了我的xyzCoord:

The output I expect is that xyzCoord should not be affected because I make a duplicate (toAdd) and then modify that. Strangely enough this loop does affect my xyzCoord:

输出为:

[[5.818, 0.0, 0.0], [0.0, 5.818, 0.0], [0.0, 0.0, 5.818]]

[[0.0, 0.0, 0.0], [2.909, 2.909, 0.0], ...

[[5.818, 0.0, 0.0], [8.727, 2.909, 0.0], ...

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就上下文而言，我的想法是我最终希望使用转置后的值制作一个单独的列表，然后最终创建一个插值列表，但是这部分使我失望. IE.我理想地想创建: [[0.0，0.0，0.0]，[5.818，0.0，0.0]，[2.909，0.0，0.0]，[8.727，2.909，0.0] ...] 然后为Y和Z做一个更大的循环.这样，我可以在X Y和Z中传播任意坐标，并且可以任意传播.

---

For context, the idea is that I want to eventually make a separate list with the transposed values and then ultimately create an intercalated list but this part is holding me up. I.e. I would ideally like to create: [[0.0, 0.0, 0.0], [5.818, 0.0, 0.0], [2.909, 0.0, 0.0], [8.727, 2.909, 0.0]...] and then make a larger loop for Y and Z. This way I could propagate some coordinates in the X Y and Z and arbitrary number of times.

推荐答案

这是关于Python的最令人惊讶的事情之一-=运算符永远不会复制任何东西！它只是将新名称附加到现有对象上.

This is one of the most surprising things about Python - the = operator never makes a copy of anything! It simply attaches a new name to an existing object.

如果要复制列表，可以使用列表的一部分.切片运算符做进行复制.

If you want to make a copy of a list, you can use a slice of the list; the slicing operator does make a copy.

toAdd=xyzCoord[i][:]

您还可以从 copy模块复制对象.

You can also use copy or deepcopy from the copy module to make a copy of an object.

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