python 进阶 单例模式

# 数据库连接的例子
class ConnectionPool:

     __instance = None

     def __init__(self):
         self.ip = "198.162.1.1"
         self.port = 3306
         self.pwd =  "123456"
         self.usr =  "xxxx"
         # 去连接
         self.conn_list = [1,2,3,4,5,6,7,8,9,10] 
          
     @staticmethod
     def get_instance():
         if ConnectionPool.__instance:
             return ConnectionPool.__instance
         else:
             # 创建一个对象，并保存在__instance
             ConnectionPool.__instance = ConnectionPool()
             return ConnectionPool.__instance

     def get_connection(self):
         #获取连接
         import random 
         r = random.randrange(1, 11)
         return r

     obj1 = ConnectionPool.get_instance()
     print(obj1)
     obj2 = ConnectionPool.get_instance()
     print(obj2)
     p = obj1. get_connection()
     print(p)