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 __setattr__(self, name: str, value: Any):
        """Custom __setattr__ to allow access to metrics schema fields."""

        if not self._initialized:
            object.__setattr__(self, name, value)
            return

        if name not in self._metric_fields:
            raise RuntimeError(
                'Field: {} not defined in metirc schema'.format(name))

        self._values[name] = value