python mysql插入数据出错的问题，也是关于处理字符串中特殊字符的问题?报错

python操作mysql时候报错

import MySQLdb

conn=MySQLdb.connect(host='localhost',user='root',passwd='123')

cursor=conn.cursor()
u='3'
bb='<b>3:1</b>'
cursor.execute('insert into bu.test (id,log) values (%s,%s)'% (str(u),bb) )
conn.commit()
cursor.close()
conn.close()

_mysql_exceptions.ProgrammingError: (1064, "You have an error in your SQL syntax; check the manual that corresponds to your MySQL server version for the right syntax to use near '<b>3:1</b>)' at line 1")

如果把变量bb的值改为bb='3:1'会报以下错误

_mysql_exceptions.ProgrammingError: (1064, "You have an error in your SQL syntax; check the manual that corresponds to your MySQL server version for the right syntax to use near ':1)' at line 1")

所以知道肯定是bb的字符串中的特殊字符在捣蛋，这个怎么处理

bb=r'3:1' 也不行

如何处理，麻烦帮忙，谢谢啊