title: Pycharm doesn't recognise data type after chaining function calls
body: <p>I have a pandas DataFrame <code>data_one</code>, some rows of which contain string values. I wanted to exclude them and drop the NaNs. So I did</p>
  
  <pre><code>data_one = date_one.convert_objects(convert_numeric=True).dropna()
  </code></pre>
  
  <p>then Pycharm failed to recognise data_one as DataFrame so autocompletion failed.</p>
  
  <p>When I do this on REPL, i.e. <code>type(data_one)</code>, I can see it is a DataFrame.</p>
  
  <p>Anyone had some problem?</p>