title: ValueError: unsupported pickle protocol: 4 with pandas
body: <p>I get this error</p>
  
  <pre><code>ValueError: unsupported pickle protocol: 4
  </code></pre>
  
  <p>from this line of my code</p>
  
  <pre><code>full_df = pd.read_pickle('df_userID.pickle')
  </code></pre>
  
  <p>when running the script with python2.7</p>
  
  <p>(on Ubuntu 14.04.5, 3.13.0-95-generic)</p>
  
  <p>Thanks for help.</p>