title: Python, Pandas ; ValueError('window must be an integer',)
body: <p>I seem to be having this issue with Pandas code inside a Bokeh callback.</p>
  
  <p>Here's part of the output before the error. My dataframe seems normal and I'm not sure why it's upset</p>
  
  <pre><code>                     time  temperature
  0 2016-03-17 11:00:00        4.676
  1 2016-03-17 11:30:00        4.633
  2 2016-03-17 12:00:00        4.639
  3 2016-03-17 12:30:00        4.603
  4 2016-03-17 13:00:00        4.615
  5 2016-03-17 13:30:00        4.650
  6 2016-03-17 14:00:00        4.678
  7 2016-03-17 14:30:00        4.698
  8 2016-03-17 15:00:00        4.753
  9 2016-03-17 15:30:00        4.847
  ERROR:bokeh.server.protocol_handler:error handling message Message 'PATCH-DOC' (
  revision 1): ValueError('window must be an integer',)
  </code></pre>
  
  <p>And here's the code I changed from the flask embed example (<a href="https://github.com/bokeh/bokeh/tree/0.12.16/examples/howto/server_embed" rel="noreferrer">link here</a>): </p>
  
  <pre><code>def callback(attr, old, new):
          df = pd.DataFrame.from_dict(source.data.copy())
          print df[:10]
          if new == 0:
              data = df
          else:
              data = df.rolling('{0}D'.format(new)).mean()
          source.data = ColumnDataSource(data=data).data
  
      slider = Slider(start=0, end=30, value=0, step=1, title="Smoothing by N Days")
      slider.on_change('value', callback)
  </code></pre>
  
  <p>I can also include the full code if that help, but the main change I have is just a doc.add_periodic_callback() that fetches new data periodically.</p>