test.py

import subprocess
import sys
import select


cmd = 'git clone --progress https://github.com/jonmorehouse/dotfiles foobar'

p = subprocess.Popen(cmd.split(' '), stdout=subprocess.PIPE, stderr=subprocess.PIPE)
while True:
    reads = [p.stdout.fileno(), p.stderr.fileno()]

    ret = select.select(reads, [], [])
    for fd in ret[0]:
        if fd == p.stdout.fileno():
            line = p.stdout.read(24)
            sys.stdout.write(line)

        if fd == p.stderr.fileno():
            # NOTE: we can't do readline, because new lines for _some outputs_ are vertical tab delimited
            line = p.stderr.read(24)

            # this method does not exist. Unfortunately, the closest we have at
            # this level of abstraction is something like read(20). Maybe we
            # should use
            # https://docs.python.org/2/library/io.html#io.RawIOBase.readall?
            # line = p.stderr.readall()
            sys.stderr.write(line)

    if p.poll() is not None:
        break

print p.returncode