title: Python subprocess Popen parameter difference
body: <p>What's the difference between</p>
  
  <pre><code>subprocess.Popen(['cat','/path/to/file'], stdout=subprocess.PIPE, shell=True)
  </code></pre>
  
  <p>and</p>
  
  <pre><code>subprocess.Popen(['cat '+'/path/to/file'], stdout=subprocess.PIPE, shell=True)
  </code></pre>
  
  <p>?
  I'm doing this in ipython.
  For the first one, ipython just hang. Maybe not hang, but it's significantly slower.
  The second is just OK.</p>
  
  <p>Just don't know why.</p>