title: NameError: name 'os' is not defined -- os.listdir error when printing all the files in a folder
body: <p>New to python and getting an error on this very simple script:</p>
  
  <pre><code>from os import listdir
  
  all_files = os.listdir("/root/raw/")
  for file in all_files:
      print file
  </code></pre>
  
  <p>What am I doing wrong here? Looks correct according to the docs.</p>