def robotsrulesetOfDomain(self, domain):
		'''检查domain是否在数据库中,
			否 --> (False, None)
			是 --> (True, 数据库中存储的robots.txt内容)
		'''
		exist = False
		cur = self.conn.cursor()
		# 是否存在
		cur.execute("SELECT 1 FROM Domains WHERE domain=?", (domain,))
		if cur.fetchone() :
			exist = True
		# 存在的话,结果是什么
		cur.execute("SELECT rules FROM Domains,Rulesets "
			"WHERE domain=? AND Domains.did=Rulesets.did"
			,(domain,) )
		ruleset = cur.fetchone()
		return (exist, ruleset)
def wait_for_snapshot_status(self, snapshot_id, status):
        """Waits for a Snapshot to reach a given status."""
        start_time = time.time()
        old_value = value = self._get_snapshot_status(snapshot_id)
        while True:
            dtime = time.time() - start_time
            time.sleep(self.build_interval)
            if value != old_value:
                LOG.info('Value transition from "%s" to "%s"'
                         'in %d second(s).', old_value,
                         value, dtime)
            if (value == status):
                return value

            if dtime > self.build_timeout:
                message = ('Time Limit Exceeded! (%ds)'
                           'while waiting for %s, '
                           'but we got %s.' %
                           (self.build_timeout, status, value))
                raise exceptions.TimeoutException(message)
            time.sleep(self.build_interval)
            old_value = value
            value = self._get_snapshot_status(snapshot_id)