code: def logger(self) -> Logger:
          
          if self._logger is None:
              self._logger = create_logger(self)
          return self._logger
docs: A :class:`logging.Logger` logger for the app.
  
          This can be used to log messages in a format as defined in the
          app configuration, for example,
  
          .. code-block:: python
  
              app.logger.debug("Request method %s", request.method)
              app.logger.error("Error, of some kind")