[FIXED] Quotes and spaces in an argument to asyncio.create_subprocess_exec() in Windows

Issue

I need to call a subprocess from an asyncio Python program running on Windows as such:

process.exe -SomeNormalArg -SomeArgField="Some Value with Spaces"

I'm currently running it like so:

config.json:

{
  "args": [
    "-SomeNormalArg",
    "-SomeArgField=\"Some Value with Spaces\""
  ] 
}

program.py:

#!/usr/bin/env python3

import asyncio
import json
args = loads(open('config.json').read())['args']


async def main():
    await asyncio.create_subprocess_exec('process.exe', *args)


if __name__ == '__main__':
    asyncio.run(main())

...But the process is spawning as process.exe -SomeNormalArg "-SomeArgField=\"Some Value with Spaces\"".

I've read the Converting an argument sequence to a string on Windows bit from the Python docs, but I can't come up with a way to make this work.

I should mention that create_subprocess_shell() with a full string of the command functions as a workaround, but it's a messy solution.

Solution

You are overquoting. The quotes in -SomeArgField="Some Value with Spaces" are only needed to prevent the shell from splitting the argument by whitespace, passing its content as separate arguments to the subprocess. Since you're using create_subrocess_exec which doesn't go through a shell, you don't have that problem to begin with and don't need to quote at all:

{
  "args": [
    "-SomeNormalArg",
    "-SomeArgField=Some Value with Spaces"
  ] 
}

That appears counter-intuitive if you're used to starting the program from a shell, but otherwise it exactly matches what you actually want to pass to the subprocess. (The subprocess won't parse quotes, the shell or the C runtime does that.)

Answered By - user4815162342