Constantly print Subprocess output while process is running

You can use iter to process lines as soon as the command outputs them: lines = iter(fd.readline, ""). Here's a full example showing a typical use case (thanks to @jfs for helping out):

from __future__ import print_function # Only Python 2.ximport subprocessdef execute(cmd):    popen = subprocess.Popen(cmd, stdout=subprocess.PIPE, universal_newlines=True)    for stdout_line in iter(popen.stdout.readline, ""):        yield stdout_line     popen.stdout.close()    return_code = popen.wait()    if return_code:        raise subprocess.CalledProcessError(return_code, cmd)# Examplefor path in execute(["locate", "a"]):    print(path, end="")

To print subprocess' output line-by-line as soon as its stdout buffer is flushed in Python 3:

from subprocess import Popen, PIPE, CalledProcessErrorwith Popen(cmd, stdout=PIPE, bufsize=1, universal_newlines=True) as p:    for line in p.stdout:        print(line, end='') # process line hereif p.returncode != 0:    raise CalledProcessError(p.returncode, p.args)

Notice: you do not need p.poll() -- the loop ends when eof is reached. And you do not need iter(p.stdout.readline, '') -- the read-ahead bug is fixed in Python 3.

See also, Python: read streaming input from subprocess.communicate().

Ok i managed to solve it without threads (any suggestions why using threads would be better are appreciated) by using a snippet from this question Intercepting stdout of a subprocess while it is running

def execute(command):    process = subprocess.Popen(command, shell=True, stdout=subprocess.PIPE, stderr=subprocess.STDOUT)    # Poll process for new output until finished    while True:        nextline = process.stdout.readline()        if nextline == '' and process.poll() is not None:            break        sys.stdout.write(nextline)        sys.stdout.flush()    output = process.communicate()[0]    exitCode = process.returncode    if (exitCode == 0):        return output    else:        raise ProcessException(command, exitCode, output)