PYTHON_FOR_REGEN only works with Python 3.10 or newer

[erlend-aasland]

On current main, PYTHON_FOR_REGEN only works with Python 3.10 or newer.

Previously, we've tried to maintain backwards compatibility with older Python versions in our build system. Last time we adjusted PYTHON_FOR_REGEN (gh-98988), we deliberately did not bump the minimal version requirements; our configure checks for Python 3.11 through Python 3.6.

While working on gh-104050, a discussion about version requirements came up, and we found out that on main, make clinic only works when PYTHON_FOR_REGEN is Python 3.10 or newer. Also, the newly introduced "generate cases script" uses pattern matching and uses newly introduced typing features. Per now, PYTHON_FOR_REGEN must be 3.10 or newer.

There are two solution to this:

1. bump the PYTHON_FOR_REGEN version requirements to 3.10 in configure
2. amend the problematic build scripts, so older Python versions are still supported

Personally, I think I'm leaning towards the former. Apparently no core dev, triager or other contributor has noticed this issue until now. No buildbot has failed (we don't test the minimum required version; perhaps we should). OTOH, I understand that it makes stuff like bootstrapping slightly more cumbersome.

Anyway, we should probably at least bump the version requirement from Python 3.6 to 3.8.

Linked PRs

• gh-104487: PYTHON_FOR_REGEN must be minimum Python 3.10 #104488

[erlend-aasland]

cc. @AlexWaygood, @JelleZijlstra, @hugovk

[AlexWaygood]

(FWIW, this issue was originally highlighted by running mypy on Tools/clinic with --python-version=3.8, which pointed out that clinic.py currently makes regular use of types.NoneType, a symbol that's new in Python 3.10.)

[erlend-aasland]

cc. @gvanrossum and @iritkatriel for Tools/cases_generator/

[erlend-aasland]

Related:

• CI: "Tests / Check if generated files are up to date" failed #99016
• gh-99016: Make build scripts compatible with Python 3.8 #99017

[gvanrossum]

I’m reluctant to have to dumb down the cases generator to 3.8. Can we please just bump the required version to 3.10? As you say there isn’t much need for earlier versions, apparently.

[erlend-aasland]

I've updated my PR with Python 3.10 as the minimum version, and I also included Python 3.12 in the list.

[sobolevn]

I also agree with bumping minimal version to 3.10 (as I said in the original issue).
I cannot imagine real-life use-cases when you need to compile the most recent Python version from source, but at the same time you don't have an access to at least 3.10

Plus, this makes writting code much more pleasant due to new typing + syntax features.

@erlend-aasland thanks for raising this! 👍

[erlend-aasland]

I cannot imagine real-life use-cases when you need to compile the most recent Python version from source, but at the same time you don't have an access to at least 3.10

Bootstrapping Python on a new platform.

Come to think of it, you probably won't use PYTHON_FOR_REGEN when building from a clean check-out anyways. You'd only need it for regenerating stuff you touched, and in that case, you can point PYTHON_FOR_REGEN to for example ./python.exe in the build dir.