def is_locked(self):
        raise NotImplemented("implement in subclass")
session_expiry can be an integer, in seconds, to set the default expiration
dataset/ETHPy150Open openstack/pylockfile/lockfile/__init__.py/LockBase.is_locked--crossover with--dataset/ETHPy150Open uwdata/termite-data-server/web2py/gluon/contrib/redis_session.py/RedisClient.__init__