code: def raise_not_found(self, environ, msg):
          
          raise NotFound(response=self.rewriterapp._error_response(environ, msg))
docs: Utility function for raising a werkzeug.exceptions.NotFound execption with the supplied WSGI environment
          and message.
  
          :param dict environ: The WSGI environment dictionary for the request
          :param str msg: The error message