Disable Python 3.6

[ischoegl]

Changes proposed in this pull request

• Disable Python 3.6 (which will stop working after Add package workflow #1158)
• Reformat some build messages during Python checks

If applicable, provide an example illustrating new features this pull request is introducing

Checklist

• The pull request includes a clear description of this code change
• Commit messages have short titles and reference relevant issues
• Build passes (scons build & scons test) and unit tests address code coverage
• Style & formatting of contributed code follows contributing guidelines
• The pull request is ready for review

[bryanwweber]

I think we should have a check at the top of SConstruct as well that the Python running SCons is >=3.7. But that can wait until after 2.6, I suppose, since it would preclude system Pythons from even running SCons and we're not using (nor will we add any, I bet) 3.7-specific features into the various SCons* files before 2.6 is released.

[ischoegl]

Done!

[ischoegl]

I wonder if it wouldn't be preferable to error out for Python 3.6 if python_package = 'default', and indicate that it can still be installed for python_package = 'none'. Going through the entire build/installation process only to realize that Python was automatically skipped is not ideal ...

[speth]

As a result of #1158, the requirement of Python 3.7 or newer applies to the Python interpreter running scons. If you try to build using Python 3.6, you will get the error:

scons: Reading SConscript files ...
  File "/src/cantera/site_scons/buildutils.py", line 1

    from __future__ import annotations
                                     ^

SyntaxError: future feature annotations is not defined

I don't think you'll ever get to the error handling added here except in the somewhat unlikely case where scons is running using Python 3.7+ but python_cmd has been explicitly pointed to an older Python installation.

The two options I see for providing a more helpful are either:

• Put an end of line comment after from __future__ import annotations.
• Check the Python version before importing buildutils in SConstruct

[bryanwweber]

• Check the Python version before importing buildutils in SConstruct

This would be my preference using sys.version

[ischoegl]

Check the Python version before importing buildutils in SConstruct

Np. What I had worked well prior to merging #1158. I added the check as requested, but left the version decision separate from the pre-existing checks.

[codecov]

Codecov Report

Merging #1222 (790af21) into main (4bfd2a8) will increase coverage by 0.03%.
The diff coverage is n/a.

❗ Current head 790af21 differs from pull request most recent head 1cc232e. Consider uploading reports for the commit 1cc232e to get more accurate results

@@            Coverage Diff             @@
##             main    #1222      +/-   ##
==========================================
+ Coverage   65.44%   65.47%   +0.03%     
==========================================
  Files         320      327       +7     
  Lines       46321    46349      +28     
  Branches    19688    19688              
==========================================
+ Hits        30315    30349      +34     
  Misses      13475    13475              
+ Partials     2531     2525       -6     

Impacted Files	Coverage Δ
src/kinetics/RxnRates.cpp	78.26% <0.00%> (-14.47%)	⬇️
include/cantera/kinetics/ReactionData.h	76.00% <0.00%> (-8.22%)	⬇️
src/kinetics/Arrhenius.cpp	95.34% <0.00%> (-3.65%)	⬇️
include/cantera/kinetics/Falloff.h	74.57% <0.00%> (-3.41%)	⬇️
include/cantera/kinetics/RxnRates.h	90.90% <0.00%> (-2.43%)	⬇️
include/cantera/kinetics/ReactionRate.h	84.09% <0.00%> (-2.28%)	⬇️
src/kinetics/InterfaceRate.cpp	91.07% <0.00%> (-1.42%)	⬇️
include/cantera/kinetics/InterfaceRate.h	84.33% <0.00%> (-1.20%)	⬇️
src/kinetics/Reaction.cpp	81.14% <0.00%> (-0.18%)	⬇️
src/zeroD/Reactor.cpp	81.31% <0.00%> (ø)
... and 25 more

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[speth]

Thanks, @ischoegl. Feel free to merge once the CI passes.