Stream stdout from a Python subprocess

counter.sh

#!/bin/bash

for i in `seq 1 10`; do
  echo $i

  if [ "$i" = "5" ]; then
    >&2 echo "Error!"
    exit 1
  fi

  sleep 1
done

stream-stdout.py

import subprocess


def chomp(string):
    while string.endswith("\n"):
        string = string[:-1]

    return string


if __name__ == '__main__':
    command = "./counter.sh"
    print(f"Command: {command}")

    process = subprocess.Popen(command,
                               stderr=subprocess.PIPE,
                               stdout=subprocess.PIPE
                               )

    for stdout in iter(process.stdout.readline, b''):
        stdout = chomp(stdout.decode())
        print(stdout)

    # Unfortunately this solution does not merge stdout and stderr streams
    for stderr in iter(process.stderr.readline, b''):
        stderr = chomp(stderr.decode())
        print(stderr)
        
    # This handles a rare case where stdout and stderr are finished streaming but
    # the process is not complete and the returncode property has not been set
    process.wait()

    # Throw exception if process returns a non-zero exit code
    if process.returncode is not 0:
        raise Exception(
            f"'{command}' exited with non-zero code: {process.returncode}")