Make intern! & py_format! strings immortal

[bschoenmaeckers]

No description provided.

[codspeed-hq]

Merging this PR will improve performance by 19.01%

⚡ 1 improved benchmark
✅ 98 untouched benchmarks
⏩ 1 skipped benchmark¹

Performance Changes

	Benchmark	BASE	HEAD	Efficiency
⚡	format_simple	368.6 ns	309.7 ns	+19.01%

---

_{Comparing bschoenmaeckers:intern-immortal (c244ede) with main (9072f6c)}

Footnotes

1. 1 benchmark was skipped, so the baseline result was used instead. If it was deleted from the codebase, click here and archive it to remove it from the performance reports. ↩

[ngoldbaum]

If you're interested in making things immortal, Python 3.15 will have PyUnstable_SetImmortal, which will allow you to do this with arbitrary objects.

There's also a backport we can adapt for Python 3.13 and 3.14: python/pythoncapi-compat#164

[bschoenmaeckers]

If you're interested in making things immortal, Python 3.15 will have PyUnstable_SetImmortal, which will allow you to do this with arbitrary objects.

There's also a backport we can adapt for Python 3.13 and 3.14: python/pythoncapi-compat#164

The following docs suggest that you should not use it on strings.

https://github.com/python/cpython/blob/aa8a43d179bad5cd9fbfce63b630e2ee0bd617e4/InternalDocs/string_interning.md?plain=1#L57

[ngoldbaum]

Sorry, I wasn't trying to say it would be useful here, just as a more general comment.