In CLI (Command Line Interpreter):
A tuple has a list component then try to += that component. Since tuple doesn't allow assignment then it raises error but actually does that.
If you try actual equivalence (A=A+B) it does not.


Python 3.9.1 (tags/v3.9.1:1e5d33e, Dec  7 2020, 17:08:21) [MSC v.1927 64 bit (AMD64)] on win32
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>>>
>>> v=([1],[2])
>>> v[0]=v[0]+[3,4]
Traceback (most recent call last):
  File "<stdin>", line 1, in <module>
TypeError: 'tuple' object does not support item assignment
>>> v
([1], [2])
>>> v[0]+=[3,4]
Traceback (most recent call last):
  File "<stdin>", line 1, in <module>
TypeError: 'tuple' object does not support item assignment
>>> v
([1, 3, 4], [2])
>>>