Python 列表赋值 BUG

print(s[-2:]) s[-1][2] = candle['h'] s[-1][3] = candle['l'] print(s[-2:]) s.append(s[-1]) print(s[-2:]) s[-1][2] = candle['c'] s[-1][3] = candle['c'] print(s[-3:])

输出： [4, [5, 5, 5, 5]] [4, [5, 5, 9, 7]] [[5, 5, 9, 7], [5, 5, 9, 7]] [4, [5, 5, 6, 6], [5, 5, 6, 6]]

我改了 list 最后一个元素的值，因为后 2 个元素是相同的值，所以倒数第 2 个也被修改了？这是 Python 的 BUG 吗？

candle

Python

bug

9 条回复 • 2022-10-19 15:20:08 +08:00

ranleng

2022-10-19 14:54:34 +08:00

代码看的头疼，
大概率是同一个对象导致的

learningman

2022-10-19 14:54:55 +08:00

请自行复习值与引用

lizytalk

2022-10-19 14:59:10 +08:00

s.append(s[-1])之后，s 中的后两个元素指向的是相同的 list 对象

superrichman

2022-10-19 14:59:30 +08:00

你 append 的是一个指针，s[-1]和 s[-2]都指向同一个 list 。改成 s.append(s[-1] * 1) 创建一个新的对象

huangzhe8263

2022-10-19 15:01:51 +08:00

use reference 和 use value 的问题

记得有一个可视化这个问题的网站，我去翻翻

huangzhe8263

2022-10-19 15:04:51 +08:00

找到了 https://pythontutor.com/render.html#mode=display

<iframe width="800" height="500" frameborder="0" src="https://pythontutor.com/iframe-embed.html#code=a%20%3D%20%5B1,%20%5B6,%207%5D%5D%0Aa.append%28a%5B1%5D%29%0Aa%5B1%5D.append%288%29&codeDivHeight=400&codeDivWidth=350&cumulative=false&curInstr=3&heapPrimitives=nevernest&origin=opt-frontend.js&py=3&rawInputLstJSON=%5B%5D&textReferences=false"> </iframe>

huangzhe8263

2022-10-19 15:05:12 +08:00

点开这个看一下就知道了

https://pythontutor.com/render.html#code=a%20%3D%20%5B1,%20%5B6,%207%5D%5D%0Aa.append%28a%5B1%5D%29%0Aa%5B1%5D.append%288%29&cumulative=false&curInstr=3&heapPrimitives=nevernest&mode=display&origin=opt-frontend.js&py=3&rawInputLstJSON=%5B%5D&textReferences=false

lz24xg

2022-10-19 15:07:35 +08:00

感谢，解决了

TimePPT

2022-10-19 15:20:08 +08:00

In [1]: s = [1,2,3,4,[5,5,5,5]]

In [2]: candle = {'h':9, 'l':7, 'c':6}

In [3]: s[-1][2] = candle['h']

In [4]: s[-1][3] = candle['l']

In [5]: s.append(s[-1])

In [6]: s[-1][2] = candle['c']

In [7]: s[-1][3] = candle['c']

In [8]: for i in s:
...: print(f"{i=}, {type(i)=}, {id(i)=}")
...:
i=1, type(i)=<class 'int'>, id(i)=4549804272
i=2, type(i)=<class 'int'>, id(i)=4549804304
i=3, type(i)=<class 'int'>, id(i)=4549804336
i=4, type(i)=<class 'int'>, id(i)=4549804368
i=[5, 5, 6, 6], type(i)=<class 'list'>, id(i)=4582898496
i=[5, 5, 6, 6], type(i)=<class 'list'>, id(i)=4582898496