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 draw():
    global theta
    context.clearRect(0, 0, canvas.width, canvas.height)
    line1.drawMe(context)
    line2.drawMe(context)
    line3.drawMe(context)
    #triangle1.drawMe(context)
    #triangle2.drawMe(context)
    theta += dx
    p2.x = p1.x + line1.length*math.cos(theta*degree)
    p2.y = p1.y - line1.length*math.sin(theta*degree)
    p3.x, p3.y = triangle2.setPPSS(p2,p4,link2_len,link3_len)
    p1.tag(context)