code: def _init_glyph(self, plot, mapping, properties):
          
          ret = super(SideHistogramPlot, self)._init_glyph(plot, mapping, properties)
          if not 'field' in mapping.get('fill_color', {}):
              return ret
          dim = mapping['fill_color']['field']
          sources = self.adjoined.traverse(lambda x: (x.handles.get('color_dim'),
                                                       x.handles.get('source')))
          sources = [src for cdim, src in sources if cdim == dim]
          tools = [t for t in self.handles['plot'].tools
                   if isinstance(t, BoxSelectTool)]
          if not tools or not sources:
              return
          box_select, main_source = tools[0], sources[0]
          handles = {'color_mapper': self.handles['color_mapper'],
                     'source': self.handles['source'],
                     'cds': self.handles['source'],
                     'main_source': main_source}
          axis = 'y' if self.invert_axes else 'x'
          callback = self._callback.format(axis=axis)
          if box_select.callback:
              box_select.callback.code += callback
              box_select.callback.args.update(handles)
          else:
              box_select.callback = CustomJS(args=handles, code=callback)
          return ret
docs: Returns a Bokeh glyph object.