title: How to get output from subprocess.Popen(). proc.stdout.readline() blocks, no data prints out
body: <p>I want output from execute Test_Pipe.py, I tried following code on Linux but it did not work. </p>
  
  <p><strong>Test_Pipe.py</strong></p>
  
  <pre><code>import time
  while True :
      print "Someting ..."
      time.sleep(.1)
  </code></pre>
  
  <p><strong>Caller.py</strong></p>
  
  <pre><code>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)
  </code></pre>
  
  <p>The line <code>proc.stdout.readline()</code> was blocked, so no data prints out.</p>