一、classmethod裝飾器
# 全局變量 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__)
輸出結果
<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、類的裝飾器
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__)
運行結果
<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、元類
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__)
運行結果
<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、模塊導入
# 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) # 測試代碼 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__)
運行結果
<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、重寫__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__)
運行結果
<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:前四種可以實現單例模式,但都不是絕對單例模式,可以創建新的對象,但是第五種方式是絕對單例模式,全局只能真正創建一次對象