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

重现报告中的两个 Linux 命令，并检查 CPython 如何根据 argv[0] 和 PATH 确定 sys.executable。将修改过 argv[0] 的情况作为回归场景；完成的标准是 sys.executable 标识正在运行的 Python 可执行文件，而不是空路径或无关路径。该 issue 引用了关联的 PR gh-145486。