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 __init__(self, cost_withGradients):
        super(CostModel, self).__init__()

        self.cost_type = cost_withGradients

        # --- Set-up evaluation cost
        if self.cost_type is None:
            self.cost_withGradients = constant_cost_withGradients
            self.cost_type = 'Constant cost'

        elif self.cost_type == 'evaluation_time':
            self.cost_model = GPModel()
            self.cost_withGradients = self._cost_gp_withGradients
            self.num_updates = 0
        else:
            self.cost_withGradients = cost_withGradients
            self.cost_type = 'User defined cost'