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

レポートにある2つの Linux コマンドを再現し、CPython が argv[0] と PATH から sys.executable をどのように決定するかを調査します。argv[0] を変更したケースをリグレッションシナリオとして使用します。完了の条件は、sys.executable が空のパスや無関係なパスではなく、実行中の Python 実行ファイルを示すことです。issue では関連する PR gh-145486 が参照されています。