About MySQLdb conn.autocommit(True)

by default MySQLdb autocommit is false,

You can set autocommit to True in your MySQLdb connection like this,

conn=MySQLdb.connect(host="localhost",user="root",passwd="mysql",db="dang",charset="utf8")
conn.get_autocommit()        #will return **False**
conn.autocommit(True)
conn.get_autocommit()        #Should return **True** now
cursor = conn.cursor()

I don't know if there's a specific reason to use autocommit with GAE (assuming you are using it). Otherwise, you can just manually commit.

class postcon:
    def POST(self):
        conn=MySQLdb.connect(host="localhost",user="root",passwd="mysql",db="dang",charset="utf8")  
        cursor = conn.cursor()
        n = cursor.execute("insert into d_message (mid,title,content,image) values(2,'xx','ccc','fff')")
        conn.commit() # This right here
        cursor.close()
        conn.close()
        if n:
            raise web.seeother('/')

Note that you probably should check if the insert happened successfully, and if not, rollback the commit.