python2 连接mysql获取值出现的错误TypeError: unsupported operand type(s) for /: 'float' and 'NoneType'

我这是一个获取实时汇率的方法，刚开始写法如下就是一直会报一个数据类型错误

获取汇率

def get_rate(self, time):

    # Where USD is the base currency you want to use
    url = 'https://v3.exchangerate-api.com/bulk/fa192ccf2d553fe2b4005125/USD'
    # Making our request
    try:
        sql = "SELECT rate, savetime from JD_rate"
        self.cur_test.execute(sql)
        rate= self.cur_test.fetchone()[0]
        savetime = self.cur_test.fetchone()[1].encode("utf-8")[:11]
        if savetime != time:
            response = requests.get(url)
            rate = response.json()['rates']['IDR']
            sql1 = "UPDATE JD_rate set rate='%s', savetime='%s' WHERE id = 1" % (rate, time)
            self.cur_test.execute(sql1)
            self.coon_test.commit()
        return rate
    except Exception, ex:
        traceback.print_exc()
        print ex, "get_rate"

改正后：（主要是不能在游标获取值后直接进行元组的取值，必须先进行保存定义）

获取汇率

def get_rate(self, time):

    # Where USD is the base currency you want to use
    url = 'https://v3.exchangerate-api.com/bulk/fa192ccf2d553fe2b4005125/USD'
    # Making our request
    try:
        sql = "SELECT rate, savetime from JD_rate"
        self.cur_test.execute(sql)
        result_a = self.cur_test.fetchone()[0]
        rate = result_a[0]

        savetime = result_a[1].encode("utf-8")[:11]
        if savetime != time:
            response = requests.get(url)
            rate = response.json()['rates']['IDR']
            sql1 = "UPDATE JD_rate set rate='%s', savetime='%s' WHERE id = 1" % (rate, time)
            self.cur_test.execute(sql1)
            self.coon_test.commit()
        return rate
    except Exception, ex:
        traceback.print_exc()
        print ex, "get_rate"