这段 Python 代码是什么结果？

[jmc891205]

l = (1, 2, [3, 4])
l[2] += [5, 6]

A. l 变为(1, 2, [3, 4, 5, 6])
B. 抛出 TypeError 异常: "'tuple' object does not support item assignment."
C. A 和 B 都是
D. A 和 B 都不是

[dacapoday]

B

[kindjeff]

我试了， AB 都是。

[weyou]

C

[beimingyouyu]

C

[HFcbyqP0iVO5KM05]

b = l[2]
b += [7,8]

[bukip]

AB

[LokiSharp]

>>> l = (1, 2, [3, 4])
>>> l[2] += [5, 6]
Traceback (most recent call last):
File "<string>", line 1, in <module>
TypeError: 'tuple' object does not support item assignment
>>> l
(1, 2, [3, 4, 5, 6])

[Yvette]

http://pythontutor.com/visualize.html#code=l%20%3D%20%281,%202,%20%5B3,%204%5D%29%0A%0Ab%20%3D%20l%5B2%5D%0Ab%20%2B%3D%20%5B5,%206%5D%0A%0Al%5B2%5D%20%2B%3D%20%5B5,%206%5D&cumulative=false&curInstr=4&heapPrimitives=false&mode=display&origin=opt-frontend.js&py=3&rawInputLstJSON=%5B%5D&textReferences=false

[cxyfreedom]

C

[director]

原理推荐看看 https://mp.weixin.qq.com/s?__biz=MzA3NDk1NjI0OQ==&mid=2247483930&idx=1&sn=ec52f6f0551a0c66baa5008d4cabf38c&chksm=9f76aeaca80127ba46aee8ae5ad446b93062f84cc1feeb1992e003c6ac7c7b32b3d0ce6ac96e#rd

[WangYanjie]

A, B 都是
l[2].append('MeiTiaoZhan')

[mingyun]

@director nice

[sunbeams001]

的确，这样就不报错了
b = l[2]
b += [5, 6]

[soratadori]

l = (1, 2, [3, 4])
try:
l[2] += [5, 6]
except:
print(l)
有点神奇

[NoAnyLove]

《 Fluent Python 》有详细解释这个问题

[mapleray]

http://shell909090.org/blog/archives/2761/

[mec]

元组不可变，哪怕这种赋值都不行 l[2] = l[2]。

[jmc891205]

@NoAnyLove 嘿嘿 就是在看这本书 为了它还买了 Safari Books Online 的订阅 钱包好疼 T_T

[yanzixuan]

@sunbeams001 你可以 L[2].extend([5,6])

[AkiseAru]

C 结果[5,6]也被赋值进去了？？？

[billgreen1]

@jmc891205 我订阅了 leetcode，买了 pycharm, 很想订阅 safari，但是的确贵

[seancheer]

我觉得出现这种问题明显是 python 设计的不合理，l[2] += [5, 6]；
这个表达式我个人认为应该为保证“事务的原子性”，而不应该出现上面这种报错了值又被改变了。

[lln133208]

@billgreen1 订阅 Pycharm 的？还是之前买的一个固定版本？

[billgreen1]

@lln133208 订阅的