Running Python from subprocess cross platforms

In one of my Python package offering a CLI, I added the ability to run it as python -m mypackage. Natuarally, I wanted to write a small test to make sure it worked, which used the subprocess module to run python with the -m flag. Simple enough, right?

result = subprocess.run(["python", "-m", ...], ...)

Well, when I pushed to CI, I realised that the python executable couldn’t be found on Windows… It’s probably called python.exe or somthing like that. Do I need to introduce a condition in my test depending on the platform? Surely, there must be a better way.

After a quick search, I found about sys.executable, which does exactly that. Neat!

Here is how my test looks like now:

import subprocess
import sys


def test_can_run_as_python_module():
    result = subprocess.run(
        [
            sys.executable,
            "-m",
            "mypackage",
            "--help"
        ],
        check=True,
        capture_output=True,
    )
    assert result.returncode == 0
    assert b"my-package [OPTIONS]" in result.stdout

Hope that helps!