Bug report

Pythonvenv on POSIX environments creates a bin directory with:

• python
• python{VERSION_MAJOR}
• python(VERSION_MAJOR}.{VERSION_MINOR}

When executingpython out of a venv made with the--copies argument specified (that is, it doesn't use symlinks), the calculation ofbase_executable will blindly append the basename of the executable to the value from thehome key frompyvenv.cfg, meaning base_executable = $home_dir/basename(executable)

With recent changes made in 3.11, on Linux, thehome key is determined by thebase_executable of the initial python that created the venv. Even if the venv is "nested",home will still point to the topmost non-venv python bin path.

However, this can be problematic because source installations viamake install only provide:

• python{VERSION_MAJOR}
• python(VERSION_MAJOR}.{VERSION_MINOR}

This means if "python" is invoked from a venv, the resultantbase_executable may be an invalid file that applications may be relying upon viasys._base_executable (bothvenv andvirtualenv use this value)

Most distributions do not distribute a version-less "python" as part of the divorce of python2 and python3 via guidance from PEP 394 (though some offer a convenience package to symlink it)

A suggested fix in previous discussions was to include a field in pyvenv.cfg specifying the base executable, but that may require updates to PEP 405 since there's only two documented keys for this file and other implementations such asvirtualenv would want to conform to new specifications (virtualenv already stores a base-executable key so there could be a conflict)

In lieu of that, a simplestat to check for alternatives seems reasonable without impacting startup performance overly much.

Since this affects 3.11+, it'd be nice to see a fix backported to that branch.

Example:

vfazio@Zephyrus:~/development/cpython$ ./configurevfazio@Zephyrus:~/development/cpython$ make -j12vfazio@Zephyrus:~/development/cpython$ DESTDIR=/tmp/tmp.w9Bqq4Aibx/ make installvfazio@Zephyrus:~/development/cpython$ cd /tmp/tmp.w9Bqq4Aibx/vfazio@Zephyrus:~/development/cpython$ /tmp/tmp.w9Bqq4Aibx/usr/local/bin/python3 -VPython 3.12.0a1+vfazio@Zephyrus:~/development/cpython$ /tmp/tmp.w9Bqq4Aibx/usr/local/bin/python3 -m venv --clear --copies /tmp/tmp.307I606AVh/vfazio@Zephyrus:~/development/cpython$ /tmp/tmp.307I606AVh/bin/python -c "import sys; print((sys._base_executable, sys.version))"('/tmp/tmp.w9Bqq4Aibx/usr/local/bin/python', '3.12.0a1+ (heads/vfazio-base-exec-fallback:267e1040a9, Nov  6 2022, 15:16:06) [GCC 9.4.0]')vfazio@Zephyrus:~/development/cpython$ test -e /tmp/tmp.w9Bqq4Aibx/usr/local/bin/python; echo $?1vfazio@Zephyrus:~/development/cpython$root@fe1d04cd5d49:/tmp/tmp.SfKfnBG1SH# usr/local/bin/python3 -VPython 3.11.0root@fe1d04cd5d49:/tmp/tmp.SfKfnBG1SH# mktemp -d/tmp/tmp.DDS5n25q4Croot@fe1d04cd5d49:/tmp/tmp.SfKfnBG1SH# usr/local/bin/python3 -m venv --copies --clear /tmp/tmp.DDS5n25q4C/root@fe1d04cd5d49:/tmp/tmp.SfKfnBG1SH# /tmp/tmp.DDS5n25q4C/bin/python -c "import sys; print((sys._base_executable, sys.version))"('/tmp/tmp.SfKfnBG1SH/usr/local/bin/python', '3.11.0 (main, Nov  5 2022, 11:43:28) [GCC 10.2.1 20210110]')root@fe1d04cd5d49:/tmp/tmp.SfKfnBG1SH# test -e /tmp/tmp.SfKfnBG1SH/usr/local/bin/python; echo $?1

Your environment

• CPython versions tested on: 3.11, main (3.12.0a1+)
• Operating system and architecture: Linux x86-64

related discussion and MRs:
https://bugs.python.org/issue46028
#29041
#30144

related issues:
pypa/virtualenv#2440
python-poetry/poetry#6940

• PR:gh-99204: Calculate base_executable by alternate names in POSIX venvs #99206

• PR:[3.11] gh-99204: Calculate base_executable by alternate names in POSIX venvs (GH-99206) #99340