code: def _get_deprecation_warning(self, route):
          
          result = ''
          if route.deprecated:
              msg = '{} is deprecated.'.format(fmt_route_func(route))
              if route.deprecated.by:
                  msg += ' Use {}.'.format(fmt_var(route.deprecated.by.name))
              result = ' __deprecated_msg("{}")'.format(msg)
          return result
docs: Returns a deprecation tag / message, if route is deprecated.