Python連結MySQL中沒有長連結的概念，但我們可以利用mysql的ping機制，來實現長連結功能~
思路:

    1 python mysql 的cping 函式會校驗連結的可用性,如果連線不可用將會產生異常
    2 利用這一特性，構造一個連線丟失的迴圈，不斷嘗試連線資料庫，直到連線恢復
    3 使用這樣的機制不需要關閉資料庫功能,對於駐留程序，有大量資料進行寫操作時，很有用途

#!/usr/bin/env python  
# -*-coding:UTF-8-*-  
import sys,MySQLdb,traceback  
import time  
class mysql
 
:  
    def __init__ (self,  
                  host   = '',  
                  user   = '',  
                  passwd = '',  
                  db     = '',  
                  port   = 3306,  
                  charset= 'utf8'  
                  ):  
        self.host   = host  
        self.user   = user  
        self.passwd = passwd  
        self.db     = db  
        self.port   = port  
        self.charset= charset  
        self.conn   = None
 
  
        self._conn()  

    def _conn (self):  
        try:  
            self.conn = MySQLdb.Connection(self.host, self.user, self.passwd, self.db, self.port , self.charset)  
            return True  
        except :  
            return False  

    def _reConn (self,num = 28800,stime = 3): #重試連線總次數為1天,這裡根據實際情況自己設定,如果伺服器宕機1天都沒發現就......  
 

        _number = 0  
        _status = True  
        while _status and _number <= num:  
            try:  
                self.conn.ping()       #cping 校驗連線是否異常  
                _status = False  
            except:  
                if self._conn()==True: #重新連線,成功退出  
                    _status = False  
                    break  
                _number +=1  
                time.sleep(stime)      #連線不成功,休眠3秒鐘,繼續迴圈，知道成功或重試次數結束  

    def select (self, sql = ''):  
        try:  
            self._reConn()  
            self.cursor = self.conn.cursor(MySQLdb.cursors.DictCursor)  
            self.cursor.execute (sql)  
            result = self.cursor.fetchall()  
            self.cursor.close ()  
            return result  
        except MySQLdb.Error,e:  
            #print "Error %d: %s" % (e.args[0], e.args[1])  
            return False  

    def select_limit (self, sql ='',offset = 0, length = 20):  
        sql = '%s limit %d , %d ;' % (sql, offset, length)  
        return self.select(sql)  

    def query (self, sql = ''):  
        try:  
            self._reConn()  
            self.cursor = self.conn.cursor(MySQLdb.cursors.DictCursor)  
            self.cursor.execute ("set names utf8") #utf8 字符集  
            result = self.cursor.execute (sql)  
            self.conn.commit()  
            self.cursor.close ()  
            return (True,result)  
        except MySQLdb.Error, e:  
            return False  

    def close (self):  
        self.conn.close()  

if __name__=='__main__':  
    my = mysql('localhost','root','password','database',3306)  
    print my.select_limit('select * from sdb_admin_roles',1,1)  
    #my.close()