While working on `RustPython` (original issue: https://github.com/RustPython/RustPython/issues/2840), I've noticed that `tuple` in CPython has explicit tests that `id` does not change when multiplied by `1`, related: - https://github.com/python/cpython/blob/64a7812c170f5d46ef16a1517afddc7cd92c5240/Lib/test/seq_tests.py#L322 - https://github.com/python/cpython/blob/64a7812c170f5d46ef16a1517afddc7cd92c5240/Lib/test/seq_tests.py#L286-L287 But, I cannot find similar tests for `str` and `bytes` which also have the same behavior: - `str`: https://github.com/python/cpython/blob/64a7812c170f5d46ef16a1517afddc7cd92c5240/Objects/unicodeobject.c#L12709-L12710 - `bytes`: https://github.com/python/cpython/blob/64a7812c170f5d46ef16a1517afddc7cd92c5240/Objects/bytesobject.c#L1456-L1458 Code: ```python >>> b = b'abc' >>> id(b), id(b * 1), id(b) == id(b * 1) (4491073360, 4491073360, True) >>> s = 'abc' >>> id(s), id(s * 1), id(s) == id(s * 1) (4489513776, 4489513776, True) ``` If tests are indeed missing and should be added, I would love to contribute them.

Perhaps it would be better to convert existing such tests to @cpython_only, since as far as I know, id() and `is` are implementation-defined for immutable objects.

Dennis, there's an existing issue on making the test suite more pypy-compatible: https://bugs.python.org/issue25130 In that issue Maciej says pypy adopted a policy to adjust tests when they have to so I'd say that unless we get a report on which additional tests should be marked as cpython_only, I wouldn't proactively do it myself. In fact, a RustPython core dev is specifically asking for more tests here so I don't see why we shouldn't accommodate that.

 New changeset a2ce538e16d5e3a6168704366bdd7a8c5af29881 by Nikita Sobolev in branch 'main': bpo-44891: Tests `id` preserving on `* 1` for `str` and `bytes` (GH-27745) https://github.com/python/cpython/commit/a2ce538e16d5e3a6168704366bdd7a8c5af29881 

 New changeset 45a97d91a42795fb0b220e67ee25a14b940c7e50 by Miss Islington (bot) in branch '3.10': bpo-44891: Tests `id` preserving on `* 1` for `str` and `bytes` (GH-27745) https://github.com/python/cpython/commit/45a97d91a42795fb0b220e67ee25a14b940c7e50 

I opted for landing this and backporting to 3.10 to increase visibility. There will be a NEWS entry about this so if any alt implementations have issues with this test, they can reach us and we'll adapt. Thanks, Nikita! ✨ 🍰 ✨