New submission from Ian Lee <ianlee1...@gmail.com>: Hi there - I admit that I don't really understand the internals here, so maybe there is a good reason for this, but I thought it was weird when I just ran across it.
If I create a new class `A`, and set it's `__slots`: ```python ➜ ~ docker run -it python:3.10 Python 3.10.2 (main, Jan 26 2022, 20:07:09) [GCC 10.2.1 20210110] on linux Type "help", "copyright", "credits" or "license" for more information. >>> class A(object): ... __slots__ = ["foo"] ... >>> A.__slots__ ['foo'] ``` If I then go to add a new attribute to extend it on the class, that works: ```python >>> A.__slots__ += ["bar"] >>> A.__slots__ ['foo', 'bar'] ``` But then if I create an instance of that class, and try to update `__slots__` on that instnace, I get an AttributeError that `__slots__` is read-only, and yet it still is updating the `__slots__` variable: ```python >>> a = A() >>> a.__slots__ ['foo', 'bar'] >>> a.__slots__ += ["baz"] Traceback (most recent call last): File "<stdin>", line 1, in <module> AttributeError: 'A' object attribute '__slots__' is read-only >>> a.__slots__ ['foo', 'bar', 'baz'] >>> A.__slots__ ['foo', 'bar', 'baz'] ``` Maybe there is a good reason for this, but I was definitely surprised that I would get a "this attribute is read-only" error, and yet still see that attribute updated. I first found this in python 3.8.5, but I also tested using docker to generate the above example using docker python:3.10 which gave me python 3.10.2. Cheers! ---------- components: Library (Lib) messages: 411886 nosy: IanLee1521 priority: normal severity: normal status: open title: __slots__ updates despite being read-only type: behavior versions: Python 3.10, Python 3.8 _______________________________________ Python tracker <rep...@bugs.python.org> <https://bugs.python.org/issue46550> _______________________________________ _______________________________________________ Python-bugs-list mailing list Unsubscribe: https://mail.python.org/mailman/options/python-bugs-list/archive%40mail-archive.com
