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@vstinner, @colesbury: please review the changes made to this pull request.

I don't think the remaining critical sections are needed either.

Okay, after thinking about it I see what you mean. I can close the PR if the critical sections are not needed.

@colesbury After further reflection, I actually think that you need the critical section in the remaining cases. For example, without the critical section, this code results in a data race:

from functools import partial 
from threading import Thread

p = partial(lambda: None)

def f():
    for _ in range(100):
        repr(p)

def g():
    for i in range(100):
        p.keywords[f"{i}"] = i


t1 = Thread(target=f)
t2 = Thread(target=g)

t1.start()
t2.start()

t1.join()
t2.join()

I attached the full TSan report here although it is quite long and I don't think it is that illuminating.

However, the only remaining cases are for the kw entry of the partial object. As such, a better solution might be to transition this kw dict to a frozendict (see issue #145478).

Let me know if you think it is worth continuing this PR or if we should close it.

Thanks @bkap123 for the PR, and @encukou for merging it 🌮🎉.. I'm working now to backport this PR to: 3.14.
🐍🍒⛏🤖

Sorry, @bkap123 and @encukou, I could not cleanly backport this to 3.14 due to a conflict.
Please backport using cherry_picker on command line.

cherry_picker 17eb0354ff3110b27f811343c2d4b3c85f2685d5 3.14

Thank you!
Let's merge since a part of this can be backported to 3.14, which doesn't have frozendict.

GH-145879 is a backport of this pull request to the 3.14 branch.