#!/usr/bin/python
 
from  subprocess import *                        
p = Popen(["cat", "-n"], bufsize=1024,stdin=PIPE, 
                    stdout=PIPE, close_fds=True) 

(fin, fout) =  (p.stdin, p.stdout)                                                 
for i in range(10): 
   fin.write("line" + str(i))
   fin.write('\n')
   fin.flush()
   print fout.readline(),