Echo call to VLC bash using subprocess.Popen on Linux

[Gribouillis]

There is an old code that I used in Linux for certain cases when stdout blocks with subprocess. It uses socketpair() and select(). Here is an example involving two scripts a.py and b.py (launched by a.py which reads its output), but it also works when the second process is not a python program. I already posted this in other forums but I think it's a nice trick to know

##################################
# a.py

import subprocess
import socket
import select

esock, echildsock = socket.socketpair()
osock, ochildsock = socket.socketpair()
p = subprocess.Popen(['python3','b.py'], 
    stderr=echildsock.fileno(),
    stdout=ochildsock.fileno())

while p.poll() is None:
    r, w, x = select.select([esock, osock],[],[], 1.0)
    if not r:
        continue # timed out
    for s in r:
        print('stdout ready' if s is osock else 'stderr ready')
        data = s.recv(1024)
        print('received', data.decode('utf8'))
osock.shutdown(socket.SHUT_RDWR)
osock.close()
esock.shutdown(socket.SHUT_RDWR)
esock.close()

##################################
# b.py

res = input('???')
print('in b:', res)