Helper for concrete methods creating session instances.

        :rtype: :class:`~google.cloud.spanner_v1.session.Session`
        :returns: new session instance.

def _new_session(self):
        """Helper for concrete methods creating session instances.

        :rtype: :class:`~google.cloud.spanner_v1.session.Session`
        :returns: new session instance.
        """
        if self.labels:
            return self._database.session(labels=self.labels)
        return self._database.session()