title: Python bokeh CustomJS callback update DataTable widget
body: <p>How can I update the values of my <code>DataTable</code> widget using <code>Select</code> widget?
  Here is my sample code:</p>
  
  <pre><code>import pandas as pd
  from bokeh.io import show
  from bokeh.layout import column
  from bokeh.models import ColumnDataSource, CustomJS, Select
  from bokeh.models.widgets import DataTable, TableColumn
  
  df = pd.DataFrame({'a': range(10,50), 'b': range(110,150)})
  
  source_foo = ColumnDataSource(data=df.loc[df['a'] &lt; 25])
  source_bar = ColumnDataSource(data=df.loc[df['a'] &gt; 25])
  source_fill = ColumnDataSource(data=df.loc[df['a'] &lt; 25])
  
  table_columns = [TableColumn(field=i, title=i) for i in ['a', 'b']]
  
  select = Select(title='Selected value:', value='foo', options=['foo', 'bar'])
  
  update = CustomJS(args=dict(source_fill=source_fill, source_foo=source_foo,
          source_bar=source_bar), code="""
  
      var data_foo = source_foo.data;
      var data_bar = source_bar.data;
      var data_fill = source_fill.data;
      var f = cb_obj.value;
      var list = ['a', 'b']
  
      if (f == 'foo') {
          for(var i = 0, size = list.length; i &lt; size ; i++) {
              var e = list[i];
              delete data_fill[e];
              data_fill[e] = data_foo[e];
          }
      }
      if (f == 'bar') {
          for(var i = 0, size = list.length; i &lt; size ; i++) {
              var e = list[i];
              delete data_fill[e];
              data_fill[e] = data_bar[e];
          }
      }
  
      source_fill.change.emit();
      """)
  
  select.js_on_change('value', update)
  
  data_table = DataTable(source=source_fill, columns=table_columns, width=150,
      height=300, row_headers=False, selectable=False)
  
  layout = column(select, data_table)
  
  bio.show(layout)
  </code></pre>
  
  <p>Here the data values are not changing if <code>selectable=False</code>. If I set <code>selectable=True</code> then the first row is refreshed. If I reorder one of the columns of <code>DataTable</code> (regardless of <code>selectable</code>) then the values are refreshed. How can refreshing be forced automatically?</p>
  
  <p>Thank you!</p>