Performance regression of pathlib.Path hashing

Bug report

Bug description:

Converting a list of pathlib.Path objects to a set() takes significantly more time in python 3.12 and beyond compared to 3.11.

The below code is a minimal reproduction:

from pathlib import Path
import time
import sys

print(sys.version)

# make 6000 paths as a string
paths_str = ["/tmp/foo/bar/{i}" for i in range(1000, 7000)]

t = time.perf_counter()
# convert it to a list of Path objects
paths_path = [Path(path) for path in paths_str]

elapsed = time.perf_counter() - t
print(f"List construct: {int(elapsed * 1000)} msec")

# convert list to set
t = time.perf_counter()
set(paths_path)
elapsed = time.perf_counter() - t
print(f"Set conversion: {int(elapsed * 1000)} msec")


# extra step: convert list to set (demonstrate caching makes it faster)
t = time.perf_counter()
set(paths_path)
elapsed = time.perf_counter() - t
print(f"Set conversion (cached): {int(elapsed * 1000)} msec")

It shows with 3.12:

3.12.11 (main, Jun  3 2025, 15:41:47) [GCC 14.3.0]
List construct: 5 msec
Set conversion: 28 msec
Set conversion (cached): 1 msec

With 3.14rc1 (similar):

3.14.0rc1 (main, Jul 22 2025, 16:42:44) [GCC 14.3.0]
List construct: 4 msec
Set conversion: 26 msec
Set conversion (cached): 1 msec

But with python 3.11 (faster):

3.11.13 (main, Jun  3 2025, 18:38:25) [GCC 14.3.0]
List construct: 12 msec
Set conversion: 8 msec
Set conversion (cached): 1 msec

I also found that not only hash() got worse but str() as well - if you replace the set() call with a [str(p) for p in paths_path].

I found a possible candidate for this issue, but that's more just a theory, I could not test it:
https://github.com/python/cpython/commit/a68e585c8b7b27323f67905868467ce0588a1dae

Could you please check what causes this?
I think newer python versions should not make the code slower, pathlib.Path is a great object (much superior than str) and now using lots of paths with a set or dict (which are also powerful data structures) kills the performance.

If you need any help, let me know.

Thank you,
Zsolt

CPython versions tested on:

3.12

Operating systems tested on:

Linux

Linked PRs

• gh-138645

Commencez par le benchmark signalé de pathlib.Path, en comparant le hashing et la conversion en chaîne avec Python 3.11, 3.12 et 3.14. Examinez le commit suspect a68e585c8b7b27323f67905868467ce0588a1dae et la PR associée gh-138645. La tâche est terminée lorsque la régression est identifiée et que des performances comparables pour les opérations sur les sets, le hash et la conversion en chaîne sont rétablies.