python 实现单例模式的5种方法

这篇文章主要介绍了python 实现单例模式的5种方法，帮助大家更好的理解和学习python 设计模式，感兴趣的朋友可以了解下

一、classmethod装饰器

 # 全局变量 ip = '192.168.13.98' port = '3306' class MySQL: __instance = None def __init__(self, ip, port): self.ip = ip self.port = port @classmethod def instance(cls, *args, **kwargs): if args or kwargs: cls.__instance = cls(*args, **kwargs) return cls.__instance obj1 = MySQL.instance(ip, port) obj2 = MySQL.instance() obj3 = MySQL.instance() print(obj1) print(obj2, obj2.__dict__) print(obj3, obj3.__dict__)

输出结果

{'ip': '192.168.13.98', 'port': '3306'}
{'ip': '192.168.13.98', 'port': '3306'}

二、类的装饰器

 def singlegon(cls): _instance = cls(ip, port) def wrapper(*args, **kwargs): if args or kwargs: return cls(*args, **kwargs) return _instance return wrapper @singlegon class MySQL1: def __init__(self, ip, port): self.ip = ip self.port = port obj1 = MySQL1() obj2 = MySQL1() obj3 = MySQL1('1.1.1.3', 8080) print(obj1) print(obj2, obj2.__dict__) print(obj3, obj3.__dict__)

运行结果

{'ip': '192.168.13.98', 'port': '3306'}
{'ip': '1.1.1.3', 'port': 8080}

三、元类

 class Mymetaclass(type): def __init__(self, class_name, class_bases, class_dic): super().__init__(class_name, class_bases, class_dic) self.__instance = self(ip, port) def __call__(self, *args, **kwargs): if args or kwargs: obj = self.__new__(self) self.__init__(obj, *args, **kwargs) self.__instance = obj return self.__instance class MySQL2(metaclass=Mymetaclass): def __init__(self, ip, port): self.ip = ip self.port = port obj1 = MySQL2() obj2 = MySQL2() obj3 = MySQL2('1.1.1.3', 80) print(obj1) print(obj2, obj2.__dict__) print(obj3, obj3.__dict__)

运行结果

{'ip': '192.168.13.98', 'port': '3306'}
{'ip': '1.1.1.3', 'port': 80}

四、模块导入

 # instance.py class MySQL: def __init__(self, ip, port): self.ip = ip self.port = port ip = '192.168.13.98' port = 3306 instance = MySQL(ip, port) # 测试代码 import os, sys sys.path.append(os.path.dirname(os.path.dirname(__file__))) from test import instance obj1 = instance.instance obj2 = instance.instance obj3 = instance.MySQL('1.1.1.3', 80) print(obj1) print(obj2, obj2.__dict__) print(obj3, obj3.__dict__)

运行结果

{'ip': '192.168.13.98', 'port': 3306}
{'ip': '1.1.1.3', 'port': 80}

五、重写__new__()

 class MySQL3(object): __instance = None __first_init = True def __init__(self, ip, port): if self.__first_init: self.ip = ip self.port = port self.__first_init = False def __new__(cls, *args, **kwargs): if not cls.__instance: cls.__instance = object.__new__(cls) return cls.__instance obj1 = MySQL3(ip, port) obj2 = MySQL3(ip, port) obj3 = MySQL3('1.1.1.3', 80) print(obj1) print(obj2, obj2.__dict__) print(obj3, obj3.__dict__)

运行结果