sys.executable is sometimes wrong

Bug report

Bug description:

On Linux, sys.executable is determined using argv[0], and trying to find that in the PATH. This presumes that the Python interpreter has been started by a shell that interprets PATH in the canonical way. There is no guarantee that this happens at all, so sys.executable may point to something completely different, or is even the empty string.

As an example:

bash -c 'exec -a whatever python -c "import sys;print(sys.executable)"'

should output the path of the Python executable, but simply outputs nothing.

Even worse, one can make Python output a wrong executable, as in

bash -c 'exec -a /usr/bin/python python -c "import sys;print(sys.executable)"'

CPython versions tested on:

CPython main branch

Operating systems tested on:

Linux

Linked PRs

• gh-145486

Reproduce los dos comandos de Linux del informe e inspecciona cómo CPython determina sys.executable a partir de argv[0] y PATH. Usa los casos con argv[0] alterado como escenarios de regresión; se considera terminado cuando sys.executable identifica el ejecutable de Python en ejecución en lugar de una ruta vacía o no relacionada. El issue hace referencia al PR vinculado gh-145486.