How to get output from subprocess.Popen(). proc.stdout.readline() blocks, no data prints out

Question

I want output from execute Test_Pipe.py, I tried following code on Linux but it did not work.

Test_Pipe.py

import time
while True :         


        

Answer 1

Nadia's snippet does work but calling read with a 1 byte buffer is highly unrecommended. The better way to do this would be to set the stdout file descriptor to nonblocking using fcntl

fcntl.fcntl(
    proc.stdout.fileno(),
    fcntl.F_SETFL,
    fcntl.fcntl(proc.stdout.fileno(), fcntl.F_GETFL) | os.O_NONBLOCK,
)

and then using select to test if the data is ready

while proc.poll() == None:
    readx = select.select([proc.stdout.fileno()], [], [])[0]
    if readx:
        chunk = proc.stdout.read()
        print chunk

She was correct in that your problem must be different from what you posted as Caller.py and Test_Pipe.py do work as provided.

• https://derrickpetzold.com/p/capturing-output-from-ffmpeg-python/