Return a session to the pool.

        Never blocks:  if the pool is full, the returned session is
        discarded.

        :type session: :class:`~google.cloud.spanner_v1.session.Session`
        :param session: the session being returned.

def put(self, session):
        """Return a session to the pool.

        Never blocks:  if the pool is full, the returned session is
        discarded.

        :type session: :class:`~google.cloud.spanner_v1.session.Session`
        :param session: the session being returned.
        """
        try:
            self._sessions.put_nowait(session)
        except queue.Full:
            try:
                session.delete()
            except NotFound:
                pass