title: Return key in process
body: <p>The code was run as:</p>
  
  <pre><code>u = subprocess.Popen(['process','abc','def','','ghi','jkl'], stdin=subprocess.PIPE, stdout=subprocess.PIPE, stderr=subprocess.PIPE)
  </code></pre>
  
  <p>It doesn't work below due to an error occurred:</p>
  
  <pre><code>ValueError: I/O operation on closed file
  </code></pre>