gh-99204: Calculate base_executable by alternate names in POSIX venvs

[vfazio]

Check to see if base_executable exists. If it does not, attempt to use known alternative names of the python binary to find an executable in the path specified by home.

If no alternative is found, previous behavior is preserved.

• Issue: sys._base_executable may not exist on posix venvs made with --copies #99204

[FFY00]

I think this is a reasonable fix, but let's see if others agree.

[zooba]

Conceptually it seems fine. Not sure whether we should mark this a "QUIRK" and aim to resolve it in some other way? I'll leave that to the POSIX people to decide

[zooba]

Please don't force push changes when doing PRs. We'll squash merge at the end, but for now I have to re-review from the start because the diff is broken.

I don't have time for that right now, but if someone else signs off and the variable names are indeed fixed, they can merge.

[vfazio]

Please don't force push changes when doing PRs. We'll squash merge at the end, but for now I have to re-review from the start because the diff is broken.

I don't have time for that right now, but if someone else signs off and the variable names are indeed fixed, they can merge.

@zooba sorry about that, my mistake completely. Diff below

-                        _base_exe = basename(executable)
-                        for _candidate in (DEFAULT_PROGRAM_NAME, f'python{VERSION_MAJOR}.{VERSION_MINOR}'):
-                            _candidate += EXE_SUFFIX if EXE_SUFFIX else ''
-                            if _base_exe == _candidate:
+                        base_exe = basename(executable)
+                        for candidate in (DEFAULT_PROGRAM_NAME, f'python{VERSION_MAJOR}.{VERSION_MINOR}'):
+                            candidate += EXE_SUFFIX if EXE_SUFFIX else ''
+                            if base_exe == candidate:
                                 continue
-                            _candidate = joinpath(executable_dir, _candidate)
+                            candidate = joinpath(executable_dir, candidate)
                             # Only set base_executable if the candidate exists.
                             # If no candidate succeeds, subsequent errors related to
                             # base_executable (like FileNotFoundError) remain in the
                             # context of the original executable name
-                            if isfile(_candidate):
-                                base_executable = _candidate
+                            if isfile(candidate):
+                                base_executable = candidate
                                 break
             break
     else:

[vfazio]

would there be any concerns about me also making a PR targeting 3.11? Fixing it here means not having to work around it in downstream packages.

[miss-islington]

Thanks @vfazio for the PR, and @zooba for merging it 🌮🎉.. I'm working now to backport this PR to: 3.11.
🐍🍒⛏🤖

[bedevere-bot]

GH-99340 is a backport of this pull request to the 3.11 branch.

[zooba]

would there be any concerns about me also making a PR targeting 3.11?

We'll let the bot do it. Should backport fine, as we haven't really been working on anything new in this file