Use shutil.which() to locate gams

[khaeru]

Pursuant the suggestion from @Wegatriespython at #523 (comment), this PR adjusts the GAMSInfo class to use shutil.which to locate the Python executable.

This may help overcome certain issues encountered when using ixmp in various ways, e.g. from terminals embedded in editors.

How to review

• Install ixmp from this branch.
• Run in your terminal: ixmp show-versions.
• Run in the (I)Python command-line/notebook/REPL: import ixmp; ixmp.show_versions()
• Try various situations:
  • With GAMS installed, or not.
  • With the IXMP_GAMS_PATH environment variable set, or not.
• Report experience/results.

PR checklist

• Continuous integration checks all ✅
• Add or expand tests; coverage checks both ✅
• Add, expand, or update documentation.
• Update release notes.

[khaeru]

@glatterf42 @behnam-zakeri @Wegatriespython @Tyler-lc —as reporters of/contributors to #456 #535 and/or #563, can I ask you each to please try out this PR branch and see if it helps address the respective issues?

If not, your precise and detailed reports will help to iterate until we have something that improves on the current code.

[codecov]

Codecov Report

Attention: Patch coverage is 33.33333% with 18 lines in your changes missing coverage. Please review.

Project coverage is 31.0%. Comparing base (8a762c1) to head (02c941b).

Files with missing lines	Patch %	Lines
ixmp/tests/test_model.py	0.0%	10 Missing ⚠️
ixmp/model/gams.py	64.2%	5 Missing ⚠️
ixmp/util/__init__.py	0.0%	3 Missing ⚠️

❗ There is a different number of reports uploaded between BASE (8a762c1) and HEAD (02c941b). Click for more details.

HEAD has 166 uploads less than BASE

Flag	BASE (8a762c1)	HEAD (02c941b)
	181	15

Additional details and impacted files

@@           Coverage Diff            @@
##            main    #564      +/-   ##
========================================
- Coverage   98.9%   31.0%   -68.0%     
========================================
  Files         44      44              
  Lines       4790    4812      +22     
========================================
- Hits        4740    1492    -3248     
- Misses        50    3320    +3270     

Files with missing lines	Coverage Δ
ixmp/util/__init__.py	39.0% <0.0%> (-59.0%)	⬇️
ixmp/model/gams.py	84.6% <64.2%> (-15.4%)	⬇️
ixmp/tests/test_model.py	0.0% <0.0%> (-100.0%)	⬇️

... and 37 files with indirect coverage changes

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[khaeru]

Not quite sure what's going on with Codecov here.

[glatterf42]

Thanks for picking this up :)

I didn't encounter this issue on my own system (yet), so not sure how well I can test this, but I'll try a few things.

[glatterf42]

Something's wrong with codecov for sure, but we could cover line 107 at least by splitting this:

match = re.search(r"^GAMS ([\d\.]+)\s*Copyright", output, re.MULTILINE)
self.version = match.group(1) if match else ...

[glatterf42]

As it stands, gams is installed on my system and added to the PATH. This is what I tried, then, after installing this branch in a fresh venv:

• ixmp show-versions shows the correct version
• In the Python console: ixmp.show_versions() shows the correct version
• In the Python console in VSCode: ixmp.show_versions() shows the correct version
• Remove gams from PATH; now I see only GAMS: no 'gams' executable in IXMP_GAMS_PATH=(not set) or the system PATH in the show-versions output
• IXMP_GAMS_PATH=~/gams/gams49.1_linux_x64_64_sfx ixmp show-versions shows the correct version
• Add gams back to PATH: everything is as before

So all this seems fine to me :)