Python之单例模式

单例模式 

内存中只存在一个实例

vim day.8-15.py

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#!/usr/bin/env python #coding:utf-8   class SqlHelper:       pass   obj1 = SqlHelper() print id(obj1) obj2 = SqlHelper() print id(obj2)                                  #两次调用id不一样   class SqlHelper2:       __static_instance = None     @classmethod     def instance(cls):         if cls.__static_instance:             return cls.__static_instance         else:             cls.__static_instance = SqlHelper2()             return cls.__static_instance   obj3 = SqlHelper2.instance() print id(obj3) obj4 = SqlHelper2.instance() print id(obj4)                                  #使用单实例,调用方法不同id一样节约内存空间

多次调用一个实例会在内存生成不同id,改变调用方法可以保证内存里面只有一个实例,节省内存空间