Python:什么时候两个变量指向内存中的同一个对象? [英] Python: When do two variables point at the same object in memory?

问题描述

这是一个例子:

l = [1, 5, 9, 3]
h = l

h[0], h[2] = h[2], h[0]

print(h) # [9, 5, 1, 3]
print(l) # [9, 5, 1, 3]

h = h*2
print(h) # [9, 5, 1, 3, 9, 5, 1, 3]
print(l) # [9, 5, 1, 3]

我的理解是调用设置 h = l 只会将 h 指向 l 指向的内存中的同一项目.那么为什么在最后 3 行中，h 和 l 没有给出相同的结果?

My understanding was that calling setting h = l would simply point h at the same item in memory that l was pointing at. So why is it that in the last 3 lines, h and l don't give the same results?

推荐答案

分配确实使 h 指向与 l 相同的项目.但是，它不会将两者永久焊接在一起.当你用 h = h * 2 改变 h 时，你告诉 Python 在内存中的其他地方构建一个双倍版本，然后让 h 指向翻倍的版本.您没有给出任何更改l的说明；仍然指向原始项目.

The assignment does make h point to the same item as l. However, it does not permanently weld the two. When you change h with h = h * 2, you tell Python to build a doubled version elsewhere in memory, and then make h point to the doubled version. You haven't given any instructions to change l; that still points to the original item.

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