def get_rate(self) -> Optional[str]:
        """
        Determine the string representation of the allowed request rate.
        """
        if not self.scope:
            msg = (
                "You must set either `.scope` or `.rate` for '%s' throttle"
                % self.__class__.__name__
            )
            raise ImproperlyConfigured(msg)

        _THROTTLE_RATES = self.get_throttling_rates()
        try:
            return _THROTTLE_RATES[self.scope]
        except KeyError as e:
            msg = "No default throttle rate set for '%s' scope" % self.scope
            raise ImproperlyConfigured(msg) from e

        Determine the string representation of the allowed request rate.
        
ninja_extra/throttling/model.py