[issue40911] Unexpected behaviour for += assignment to list inside tuple

[Steven D'Aprano]

Steven D'Aprano <steve+python at pearwood.info> added the comment:

Alas, this gotcha is the consequence of the way `+=` is defined in Python. Although the behaviour is surprising, there's nothing to fix because everything is working as expected:

* addition to a list will extend the list, as expected;
* trying to assign into a tuple will fail, as expected.

It's just the combination that is surprising.

There's even a FAQ for it:

https://docs.python.org/3/faq/programming.html#why-does-a-tuple-i-item-raise-an-exception-when-the-addition-works

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nosy: +steven.daprano
resolution:  -> not a bug
stage:  -> resolved
status: open -> closed

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Python tracker <report at bugs.python.org>
<https://bugs.python.org/issue40911>
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