python mysql使用持久链接

python链接mysql中没有长链接的概念，但我们可以利用mysql的ping机制，来实现长链接功能~

思路:

1 python mysql 的cping 函数会校验链接的可用性,如果连接不可用将会产生异常

2 利用这一特性，构造一个连接丢失的循环，不断尝试连接数据库，直到连接恢复

3 使用这样的机制不需要关闭数据库功能,对于驻留进程，有大量数据进行写操作时，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): #重试连接总次数为1天,这里根据实际情况自己设置,如果服务器宕机1天都没发现就......
_number = 0
_status = True
while _status and _number <= num:
try:
self.conn.ping()       #cping 校验连接是否异常
_status = False
except:
if self._conn()==True: #重新连接,成功退出
_status = False
break
_number +=1
time.sleep(stime)      #连接不成功,休眠3秒钟,继续循环，知道成功或重试次数结束

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()