[issue17973] '+=' on a list inside tuple both succeeds and raises an exception

[Ronald Oussoren]

Ronald Oussoren added the comment:

This is a side effect to the way the in place operators work.

Basically "a[0] += [3]" is evaluated as:

    a[0] = a[0].__iadd__([3])

The call to __iadd__ succeeds, which is why the list is updated, but you get an exception when the interpreter tries to update item 0 of the tuple.

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nosy: +ronaldoussoren

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Python tracker <report at bugs.python.org>
<http://bugs.python.org/issue17973>
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