title: Python 2.7 How to list files in a directory AND all sub directories?
body: <p>I am writing a script that lists number of lanes, words in text files and now I want to add looking for duplicates. </p>
  
  <p>right now I am using this to list all the text files in a directory:</p>
  
  <pre><code>from sys import argv 
  script, directory - argv
  files = glob.glob(directory + "/*.txt")
  </code></pre>
  
  <p>If there are any sub-folders in the directory it will not list those files. How can I do it so that it lists all files from all sub-directories as well?</p>