Check a session out from the pool.

        :type timeout: int
        :param timeout: seconds to block waiting for an available session

        :rtype: :class:`~google.cloud.spanner_v1.session.Session`
        :returns: an existing session from the pool, or a newly-created
                  session.
        :raises: :exc:`six.moves.queue.Empty` if the queue is empty.

def get(self, timeout=None):  # pylint: disable=arguments-differ
        """Check a session out from the pool.

        :type timeout: int
        :param timeout: seconds to block waiting for an available session

        :rtype: :class:`~google.cloud.spanner_v1.session.Session`
        :returns: an existing session from the pool, or a newly-created
                  session.
        :raises: :exc:`six.moves.queue.Empty` if the queue is empty.
        """
        if timeout is None:
            timeout = self.default_timeout

        ping_after, session = self._sessions.get(block=True, timeout=timeout)

        if _NOW() > ping_after:
            if not session.exists():
                session = self._new_session()
                session.create()

        return session