How to get output from subprocess.Popen(). proc.stdout.readline() blocks, no data prints out

I want output from execute Test_Pipe.py, I tried following code on Linux but it did not work.

Test_Pipe.py

import time
while True :
    print "Someting ..."
    time.sleep(.1)

Caller.py

import subprocess as subp
import time

proc = subp.Popen(["python", "Test_Pipe.py"], stdout=subp.PIPE, stdin=subp.PIPE)

while True :
    data = proc.stdout.readline() #block / wait
    print data
    time.sleep(.1)

The line proc.stdout.readline() was blocked, so no data prints out.