subproc.py

from subprocess import Popen, PIPE

def run_command():
    with Popen(['pp3.py'], stdout=PIPE, stderr=PIPE, bufsize=1, universal_newlines=True) as p:
        while p.poll() is None:
            out = p.stdout.readline()
            err = p.stderr.readline()
            print(out, end='')
            print(err, end='')


if __name__ == "__main__":
    run_command()