用Python实现如下要求

#encoding=utf-8
while True:
    try:
        score = raw_input("input the score,'exit' to stop: >>:")
        #print type(score)
        #print isinstance(score,str)

        if "exit" in score:
            break
        else:
            score = float(score)
            print "score:",score
            if score >= 90 and score <=100:
                print u"优"
            elif score>=80 and score <90:
                print u"良"
            elif score >=70 and score <80:
                print u"中"
            elif score >= 60 and score <70:
                print u"及格"
            elif score >=0 and score <60:
                print u"不及格"
            else:
                print u"请重新输入！"
    except Exception,e:
        print e
        print u"请重新输入！"
        continue