code: def handle_download_click(self, *args):
          
          self.download_button.on_click(self.handle_download_click,remove=True)
          self.download_button.description = 'Downloading ...'
          self._string = self._fileobj.read()
          self.render_string()
docs: Callback for download button. Downloads the file and replaces the button
          with a view of the file.
          :param args:
          :return: