def __missing__(self, key):
        if self.default_factory is None:
            raise KeyError(key)
        else:
            ret = self[key] = self.default_factory(name=key)
            return ret
def get_metrics(self):
        """Returns the stored metrics.

        The metrics are type checked against the set schema.

        Returns:
          Dictionary of metrics data in the format of the set schema.
        """
        artifact_utils.verify_schema_instance(self._schema, self._values)
        return self._values