python 实现单例模式的5种方法
Wuliwawa 人气:0本文着重讲解了python 实现单例模式的5种方法,有助于更直观的学习和测试python 设计模式,欢迎大家阅读
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
<main.MySQL object at 0x058D6F30>
<main.MySQL object at 0x058D6F30> {'ip': '192.168.13.98', 'port': '3306'}
<main.MySQL object at 0x058D6F30> {'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
<main.MySQL1 object at 0x04C102B0>
<main.MySQL1 object at 0x04C102B0> {'ip': '192.168.13.98', 'port': '3306'}
<main.MySQL1 object at 0x04C10310> {'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
<main.MySQL2 object at 0x04D003B0>
<main.MySQL2 object at 0x04D003B0> {'ip': '192.168.13.98', 'port': '3306'}
<main.MySQL2 object at 0x04D003D0> {'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
<day30.instance.MySQL object at 0x052B0AB0>
<day30.instance.MySQL object at 0x052B0AB0> {'ip': '192.168.13.98', 'port': 3306}
<day30.instance.MySQL object at 0x052B03F0> {'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
<main.MySQL3 object at 0x059603F0>
<main.MySQL3 object at 0x059603F0> {'ip': '192.168.13.98', 'port': '3306', '_MySQL3__first_init': False}
<main.MySQL3 object at 0x059603F0> {'ip': '192.168.13.98', 'port': '3306', '_MySQL3__first_init': False}
注:前四种可以实现单例模式,但都不是绝对单例模式,可以创建新的对象,但是第五种方式是绝对单例模式,全局只能真正创建一次对象
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