title: Remove particular permission using os.chmod
body: <p>How can we remove a particular permission for all using os.chmod ?</p>
  
  <p>In short, how can we write the below using os.chmod</p>
  
  <pre><code>chmod a-x filename
  </code></pre>
  
  <p>I do know that we can add permission to an existing one and remove also. </p>
  
  <pre><code>In [1]: import os, stat
  In [5]: os.chmod(file, os.stat(file).st_mode | stat.S_IRGRP)  # Make file group readable.
  </code></pre>
  
  <p>But I am not able to figure out the doing the all operation </p>