GeezerVison

So for the first glance, there are two questions:

1. What if the key equals to a unicode string, but has a different hash? I know it's not "supposed" to be, but that could happen and this implementation has a different behavior than a real dict.
2. The separate loop was intentional - do a quick pointer equality check first, then do the slow check. It will save us some time. I think we should keep that.

I did no go through the whole change because I don't believe we've reached to the point where we agree how to do this.

1. I don't think we need to match dict in this anomalous case.
   The dict behaviour itself depends on internal implementation details one shouldn't rely on.

   However, we can use the hash to skip PyObject_RichCompareBool calls, which seems beneficial on its own.
   (But it doesn't match dict behaviour exactly. Dict doesn't use the full hash; how much of the hash it uses depends on the internal table size.)

2. OK. (I'd be surprised if the speedup didn't matter in real-world use cases, so I went for simpler code before.)

@gaogaotiantian and/or @markshannon, your review would be appreciated, so we can get this in 3.13.

Looks good.

There is one test I'd like to added, though.
This little program now succeeds (it fails on main):

class Str(str):
    pass

def foo():
    sys._getframe().f_locals[Str("x")] = 2
    assert x == 2
    x = 1

foo()

but it doesn't seem like there is a test for this case (writing a fast local using a non-str key).
Could you add a test for this?

Will do in ~6 hours, feel free to beat me to it.

Test added. (There was one for writing a fast local using a non-str key, but not for writing a so far uninitialized local like your example, so I added that.)

Thank you for the reviews!

Thanks @encukou for the PR 🌮🎉.. I'm working now to backport this PR to: 3.13.
🐍🍒⛏🤖

Sorry, @encukou, I could not cleanly backport this to 3.13 due to a conflict.
Please backport using cherry_picker on command line.

cherry_picker 5912487938ac4b517209082ab9e6d2d3d0fb4f4d 3.13

GH-122488 is a backport of this pull request to the 3.13 branch.