title: subprocess.check_output() doesn't seem to exist (Python 2.6.5)
body: <p>I've been reading the Python documentation about the subprocess module (see <a href="http://docs.python.org/library/subprocess.html#subprocess-replacements">here</a>) and it talks about a <code>subprocess.check_output()</code> command which seems to be exactly what I need.</p>
  
  <p>However, when I try and use it I get an error that it doesn't exist, and when I run <code>dir(subprocess)</code> it is not listed.</p>
  
  <p>I am running Python 2.6.5, and the code I have used is below:</p>
  
  <pre><code>import subprocess
  subprocess.check_output(["ls", "-l", "/dev/null"])
  </code></pre>
  
  <p>Does anyone have any idea why this is happening?</p>