python一套完整的事务操作

#coding=utf-8
import sys
import MySQLdb

class TransferMoney(object):
    def __init__(self,conn):
        self.conn = conn

    #检查账户是否合法
    def check_acct_avaiable(self,acctid):
        cursor = self.conn.cursor()
        try:
            sql = "select * from account where acctid=%s" % acctid
            cursor.execute(sql)
            print "check account:" + sql
            rs = cursor.fetchall()
            if len(rs) != 1:
                raise Exception("account %s illega" % acctid)
        finally:
            cursor.close()

    #检查是否有足够的钱
    def has_enough_money(self,acctid,money):
        cursor = self.conn.cursor()
        try:
            sql = "select * from account where acctid=%s and money > %s" % (acctid,money)
            cursor.execute(sql)
            print "has enough money:" + sql
            rs = cursor.fetchall()
            if len(rs) != 1:
                raise Exception("account %s not enough money" % acctid)
        finally:
            cursor.close()

    #账户减钱
    def reduce_money(self,acctid,money):
        cursor = self.conn.cursor()
        try:
            sql = "update account set money = money-%s where acctid = %s" % (money,acctid)
            cursor.execute(sql)
            print "reduce_money:" + sql
            if cursor.rowcount != 1:
                raise Exception("reduce money fail %s" % acctid)
        finally:
            cursor.close()

    #账户加钱
    def add_money(self,acctid,money):
        cursor = self.conn.cursor()
        try:
            sql = "update account set money = money+%s where acctid = %s" % (money,acctid)
            cursor.execute(sql)
            print "add_money:" + sql
            if cursor.rowcount != 1:
                raise Exception("add money fail %s" % acctid)
        finally:
            cursor.close()
    #主执行语句
    def transfer(self,source_acctid,target_acctid,money):
        try:
            self.check_acct_avaiable(source_acctid)
            self.check_acct_avaiable(target_acctid)
            self.has_enough_money(source_acctid,money)
            self.reduce_money(source_acctid,money)
            self.add_money(target_acctid,money)
            self.conn.commit()
        except Exception as e:
            self.conn.rollback()
            raise e

if __name__ == "__main__":
    source_acctid = sys.argv[1]
    target_acctid = sys.argv[2]
    money = sys.argv[3]
    conn = MySQLdb.Connect(host = '127.0.0.1',port=3306,user='root',passwd='',db='test',charset='utf8')
    tr_money = TransferMoney(conn)

    try:
        tr_money.transfer(source_acctid,target_acctid,money)
    except Exception as e:
        print "Happen:" + str(e)
    finally:
        conn.close()