What is the correct syntax to spawn a process with "await nursery.start(trio.run_process, ...)"?

Question

I want to spawn a process and get the process-object for further processing. But I got an error when I use arguments. What am I doing wrong?

Here is my script:

import trio
from subprocess import PIPE

VAR = {'prg': None}

async def main():
    async with trio.open_nursery() as nrs:
        VAR['prg'] = await nrs.start(trio.run_process, 'cvlc -'.split(), stdin=PIPE)
        nrs.start_soon(test)

async def test():
    while VAR['prg'] is None:
        await trio.sleep(0.1)
    print(dir(VAR['prg']))
    print(type(VAR['prg'].stdin))
    await trio.sleep(2)
    VAR['prg'].terminate()

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

And this is the error-message:

Traceback (most recent call last):
  File "/media/DEV/mit_trio_loop/Test-run_process_01.py", line 28, in <module>
    trio.run(main)
  File "/home/tester/.local/lib/python3.10/site-packages/trio/_core/_run.py", line 2010, in run
    raise runner.main_task_outcome.error
  File "/media/DEV/mit_trio_loop/Test-run_process_01.py", line 16, in main
    VAR['prg'] = await nrs.start(trio.run_process, 'cvlc -'.split(), stdin=PIPE)
TypeError: Nursery.start() got an unexpected keyword argument 'stdin'

I'm stuck here. Can anyone help?

Answer 1

Use functools.partial to encapsulate the arguments. nursery.startdoesn't allow them.

        VAR['prg'] = await nrs.start(functools.partial(trio.run_process, 'cvlc -'.split(), stdin=PIPE))