Feature or enhancement

Currently, the error message for an attribute that isn't included in a class's__slots__ is harder to understand than I think it needs to be.

Python 3.12.0a0 (heads/main:4114bcc, Sep  7 2022, 19:35:54) [Clang 13.1.6 (clang-1316.0.21.2.5)] on darwinType "help", "copyright", "credits" or "license" for more information.>>>classFoo:...__slots__= ("bar",)... >>> Foo().not_an_attribute=1234Traceback (most recent call last):  File "<stdin>", line 1, in <module>AttributeError: 'Foo' object has no attribute 'not_an_attribute'

Pitch

I think the message can be improved in multiple ways and be made more similar to the error message for attribute access:

1. Make the error message contain a note as to why the assignment failed. Ideally, this would look something like

   AttributeError:'Foo'cannothaveattribute'not_an_attribute'setasitisnotincludedinits__slots__

2. Make the error message more forgiving in the case of a typo.

   >>> Foo().bat="hello world"Traceback (most recent call last):  File "<stdin>", line 1, in <module>AttributeError: 'Foo' cannot have attribute 'bat' set as it is not included in its __slots__. Did you mean: 'bar'?

3. Support more introspection on the raised AttributeError as currently name and obj are None.

Linked PRs

• gh-96663: Add a better error message for __dict__-less classes setattr #103232