Adam Cmiel added the comment:
Got it, I didn't realize that the last step of augmented assignment is (in this
case) assigning the result of __iadd__ back to the tuple.
Thanks for the explanations!
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Python tracker
Rémi Lapeyre added the comment:
Multiple steps happens at once here, first the list is extended, then the
result is written back to the tuple, at which point it raises TypeError because
you can't write to a tuple. When TypeError is raised, the list has already be
extended. The code is
Steven D'Aprano 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
New submission from Adam Cmiel :
Python version:
Python 3.8.3 (default, May 15 2020, 00:00:00)
[GCC 10.1.1 20200507 (Red Hat 10.1.1-1)] on linux
Description:
When assigning to a tuple index using +=, if the element at that index is a
list, the list is extended and a TypeError is raised.
a
