Utilizing multiprocessing.Pipe() with subprocess.Popen/run as stdin/stdout

Question

I'm currently working on a POC with the following results to be desired

python script working as a parent, meaning it will start a child process while running it
the child process is oblivious to the fact another script is running it, the very same child script can also be executed as the main script by the user
comfortable way to read the subprocess's outputs (to sys.stdout via print), and the parent's inputs will be sent to the sys.stdin (via input)

I've already done some research on the topic and I am aware that I can pass to Popen/run subprocess.PIPE, and call it a day. However I saw multiprocessing.Pipe() produces a linked socket pair which allows to send objects through them as a whole, so I don't need to get into when to stop reading a stream and continue afterward

# parent.py
import multiprocessing
import subprocess
import os

pipe1, pipe2 = multiprocessing.Pipe()
if os.fork():
    while True:
        print(pipe1.recv())
    exit() # avoid fork colision

if os.fork():
    # subprocess.run is busy wait
    subprocess.run(args['python3', 'child.py'], stdin=pipe2.fileno(), stdout=pipe2.fileno())
    exit() # avoid fork colision

while True:
    user_input = input('> ')
    pipe1.send(user_input)

# child.py

import os
import time

if os.fork:
    while True:
        print('child sends howdy')
        time.sleep(1)

with open('child.txt, 'w') as file
    while True:
        user_input = input('> ')
        # We supposedly can't write to sys.stdout because parent.py took control of it
        file.write(f'{user_input}
')

So to finally reach the essence of the problem, child.py is installed as a package, meaning parent.py doesn't call on the actual file to run the script. The subprocess is run by calling upon the package And for some bizarre reason, when child.py is a package vs a script, the code written above doesn't seem to work. child.py's sys.stdin and sys.stdout fail to work entirely, parent.py is unable to receive ANY of the child.py's prints (even sys.stdout.write() and sys.stdout.flush()), and the same applies to sys.stdin.

If anyone can shed any light on how to solve it, I would be delighted !

Side Note

When calling upon a package, you don't call upon its main.py (image it's dunder_main_dunder.py) directly. you call upon a python file which it actually starts up the package. I assume something fishy might be happening over there when that happens and that what causes the interference, but that's just a theory

Utilizing multiprocessing.Pipe() with subprocess.Popen/run as stdin/stdout

0 Answers