import subprocess, time
subproc = subprocess.Popen(['c:\python31\python.exe', 'c:/b.py'], stdin=subprocess.PIPE, shell=True) 
time.sleep(0.5)
print('start')
subproc.stdin.write('data\n')
subproc.communicate('data\n')
print('end')

import sys
print('receive...')
s = sys.stdin.readline()
print('get:', len(s), s)