scrapy采集入为库mysql数据库，只更新一个字段提示这个语法错误？

    def insert_into_info(self, conn, item):

        print ('starts...')

        ziinfo = item['zi']

        conn.execute("""select 1 from news_topic where zi = %s""", (ziinfo, ))

        ret = conn.fetchone()

        tp_id = int(conn.lastrowid)

        print ('###aa')

        if ret:

            print(u'开始更新这条数据')

            UPDATE news_topic SET bsmc = item['bsmc'] WHERE id = tp_id;

            pass

        else:

            pass