title: Update Bokeh ranges with Pandas Period objects
body: <p>Say I have a dataframe <code>line_src_yr</code> like:</p>
  
  <pre><code>Date Value
  2017 100
  2018 200
  </code></pre>
  
  <p>and a second dataframe <code>dfQtr</code> like:</p>
  
  <pre><code>Date   Value
  2017Q1  25
  2017Q2  25
  2017Q3  25
  2017Q4  25
  2018Q1  100
  2018Q2  100
  </code></pre>
  
  <p>I'd like to be able to alternate between the dataframes underlying my plot using a radio button:</p>
  
  <pre><code>QtrLineSrc=ColumnDataSource(data=dfQtr)
  line_src_yr=ColumnDataSource(data=line_df_yr)
  
  if radio_group.active==0:
      p_line.xaxis_type='datetime'             
      p_line.xaxis.formatter=DatetimeTickFormatter(days=["%Y"])
      line_src_yr.data={"Date":line_df_yr["Date"],"Value":line_df_yr['Value']}
  elif radio_group.active==1:
      line_src_yr.data=QtrLineSrc.data
      p_line.x_range=list(set(dfQtr["Date"]))
  
  radio_group=RadioGroup(labels=["Annual","Quarter"], active =0)
  radio_group.on_change('active', update)
  
  p_line=figure(plot_width= 750, plot_height=450)
  p_line.line(x="Date",y="Value", source=line_src_yr)
  </code></pre>
  
  <p>But I get</p>
  
  <blockquote>
    <p>:Error running application handler : Unrecognized range input: '[Period('2017Q3', 'Q-DEC'), Period('2018Q1', 'Q-DEC'), Period('2018Q2', 'Q-DEC'), Period('2017Q4', 'Q-DEC'), Period('2017Q1', 'Q-DEC'), Period('2018Q3', 'Q-DEC'), Period('2018Q4', 'Q-DEC'), Period('2017Q2', 'Q-DEC')]'</p>
  </blockquote>
  
  <p>I suspect its due to <code>dfQtr</code> not being <code>datetime</code>, but if I try to convert to such, it yields <code>&lt;class 'pandas._libs.tslibs.period.Period'&gt; is not convertible to datetime</code></p>