title: Python: saving objects and using pickle. extension of filename
body: <p>Hello I´m trying using the next piece of code:</p>
  
  <pre><code>import pickle 
  object = Object() 
  filehandler = open(filename, 'w') 
  pickle.dump(object, filehandler) 
  </code></pre>
  
  <p>I would like to know what should be the extension of the file 'filename'.
  Thank you!</p>