Return values that are to be shown in repr string.

def _repr_values(self):
        """Return values that are to be shown in repr string."""
        def getattr_better(obj, field):
            try:
                return getattr(obj, field)
            except AttributeError as e:
                try:
                    return getattr(obj, '_' + field)
                except AttributeError:
                    raise e

        return (getattr_better(self, attr) for attr in self._repr_attributes)