Updated logic for determining available python version string.

[matteius]

Potential fix for issue #5835

The checklist

• [X] Associated issue
• [ ] A news fragment in the news/ directory to describe this fix with the extension .bugfix.rst, .feature.rst, .behavior.rst, .doc.rst. .vendor.rst. or .trivial.rst (this will appear in the release changelog). Use semantic line breaks and name the file after the issue number or the PR #.