code: def _handle_assets(self, relpath, params):
      
      if self._settings.assets_dir:
        abspath = os.path.normpath(os.path.join(self._settings.assets_dir, relpath))
        with open(abspath, 'rb') as infile:
          content = infile.read()
      else:
        content = pkgutil.get_data(__name__, os.path.join('assets', relpath))
      content_type = mimetypes.guess_type(relpath)[0] or 'text/plain'
      self._send_content(content, content_type)
docs: Statically serve assets: js, css etc.