Use named pipes to stream answers between processes without buffering (thanks to stdbuf -o0)

named.py

import os
import shlex
import subprocess


def spawn(cmd):
    os.mkfifo("toto")
    with open("toto", "w") as f:
        process = subprocess.Popen(shlex.split(cmd), stdout=f)
    process.wait()
    os.unlink("toto")

spawn("stdbuf -o0 python test.py")

readpipe.py

from __future__ import print_function
import os
import os.path


def read_fifo(filename):
    with open(filename) as fifo:
        while os.path.exists(filename):
            print(fifo.readline(), end='')

read_fifo("toto")

test.py

#! /use/bin/python
import time

for i in range(100):
    time.sleep(0.2)
    print i