fix: str of KeyError for <3.11

[agoose77]

This fixes #2513

[codecov]

Codecov Report

Merging #2519 (3483e2b) into main (60114c5) will decrease coverage by 0.01%.
The diff coverage is 66.66%.

❗ Current head 3483e2b differs from pull request most recent head e59cb86. Consider uploading reports for the commit e59cb86 to get more accurate results

Additional details and impacted files

Impacted Files	Coverage Δ
src/awkward/_errors.py	80.27% <66.66%> (-0.59%)	⬇️

... and 3 files with indirect coverage changes

[jpivarski]

I'm uncomfortable about our class pretending to be the builtins.KeyError. It can be named KeyError, but let's make it distinguishable by __module__, so that when someone is digging into a bug, we're not making the solution harder for them.

(I'm assuming that experts who are trying to resolve bugs would know that classes can have the same name in different modules.)

[jpivarski]

I'm wary of this. It could lead to someone being very confused that this type is not KeyError for some reason.

I was thinking that we would name the class ak._errors.KeyError, so it displays its name as KeyError, but it's distinguishable by its __module__. Setting __module__ = "builtins" sounds like we're setting up for a disaster.

[agoose77]

That's fair. In general, it's not good practice to use 'is' like this, but I think you make a reasonable argument. Let's rework this in line with making our error distinguishable from the built-in.

[jpivarski]

I made a counter-edit to indicate what I meant. If we're saying its name is KeyError, then we should let its name be KeyError; module encapsulation is for making these sorts of same-name-but-distinct references.

It means that we can never use unqualified KeyError in the text of this file—it always has to be builtins.KeyError—but that's normal. Uproot's reading.py has to do that with the function named open, and ak_zip.py has to do that with the function named zip.

[agoose77]

I prefer not to shadow the KeyError builtin, as it's not something one usually overrides in a global namespace. Our AwkwardKeyError isn't something I anticipated even L3 awkward modules importing, so changing __name__ didn't both me. With some time having elapsed, I have changed my mind on that, so I'm now in favour of this change.