import sys
import time
import subprocess

command = [sys.executable, 'tok2.py']
proc = subprocess.Popen(command, stdin=subprocess.PIPE, stdout=subprocess.PIPE, stderr=subprocess.PIPE)

i=0
while proc.poll() is None:
    if i > 5:
        #Send 'exit' after 5th iteration
        proc.stdin.write(b'exit')

    print('tok1: '  + str(i))

    time.sleep(0.5)
    i=i+1

import sys
import time

ii=0
my_input =''
while True:
    my_input = sys.stdin.read()

    if my_input == b'exit':
        print('tok2: exiting')
        sys.stdout.flush()
        break

    print('tok2: ' + str(ii))
    sys.stdout.flush()
    ii=ii+1
    time.sleep(0.5)