Expose LTS_CPU in a public API

[alonme]

Description

I think we should enable users to check if the installed version of polars is LTS_CPU or not programmatically.

I suggest adding this information to pl.show_versions()

Would be happy to implement this if maintainers agree to the idea

[ritchie46]

Yes, I think we can add that show_versions.

[alonme]

Ok so i believe i found a couple of issues while working on that

1. The _POLARS_LTS_CPU isn't actually set in the build process!
   This means that the check_cpu_flags doesn't exit early - however because the _POLARS_FEATURE_FLAGS is changed to match the lts-cpu mode - everything works?

Reproduction:

> pip install polars-lts-cpu --force-reinstall --quiet
> cat .venv2/lib/python3.11/site-packages/polars/_cpu_check.py | grep "LTS_CPU = "
_POLARS_LTS_CPU = False

The problem is that the sed command replaces the "old" name of the variable _LTS_CPU and not _POLARS_LTS_CPU

polars/.github/workflows/release-python.yml

Line 178 in a0ec630

sed $SED_INPLACE 's/^_LTS_CPU = False$/_LTS_CPU = True/g' $CPU_CHECK_MODULE

2. Minor:
   the wheel seems to contain a redundant file called _cpu_check.py''

> ls .venv/lib/python3.11/site-packages/polars/_cpu_*
.venv2/lib/python3.11/site-packages/polars/_cpu_check.py   .venv2/lib/python3.11/site-packages/polars/_cpu_check.py''

@ritchie46 - I think i'll create a PR to fix issue 1, and then expose the variable in another PR - sounds alright?
regarding issue 2 - i'll open another issue?

[orlp]

I think we can remove the LTS CPU check bypass. The comment justifying it is:

# Set to True during the build process if we are building a LTS CPU version.
# The risk of the CPU check failing is then higher than a CPU not being supported.
_POLARS_LTS_CPU = False

This was initially done as a conservatism when the CPU check was introduced. However, I messed up and the code actually replaces the wrong variable as you noticed, so we were never conservative in the first place, without any issues. But now that it's been in Polars for quite a while I think we can safely say it works on polars-lts-cpu as well, and has actually diagnosed for people with CPUs that are too old even for LTS: #18956.

So at this point I would suggest making a PR that does set _POLARS_LTS_CPU correctly but removes the bypass and always runs the CPU check also on lts-cpu.

[alonme]

@orlp sounds good - i'll do that

[alonme]

@ritchie46 any chance you can build macos wheels so i can verify that the github actions change works? (there was a miss there originally so i would like to make sure all works now)

[ritchie46]

ally so i would like to make sure all works now)

You can test that on your fork.