def get_last_tid(self):
        try:
            spec = {'tid': {'$gt': 0}}
            sort = [('tid', -1)]
            row = self.db.docs.find_one(spec, sort=sort)
        except Exception as e:
            raise DatabaseException(e)
        if row:
            return row['tid']
        return 0
def __init__(self, saddr, gaddr, glen):
        self.saddr = saddr
        self.gaddr = gaddr
        self.glen = glen
        if ip_address(self.saddr).version != \
           ip_address(self.gaddr).version:
            raise ValueError('Source and group addresses must be of the '
                             'same address family.')