zoukankan      html  css  js  c++  java
  • 单例(多次实例化的结果指向同一个实例)

    # 单例模式:多次实例化的结果指向同一个实例
    # 单例模式实现方式一:
    '''
    import settings
    class MySQL:
        __instance=None
        def __init__(self, ip, port):
            self.ip = ip
            self.port = port
        @classmethod
        def from_conf(cls):
            if cls.__instance is None:
                cls.__instance=cls(settings.IP, settings.PORT)
            return cls.__instance
    obj1=MySQL.from_conf()
    obj2=MySQL.from_conf()
    obj3=MySQL.from_conf()
    # obj4=MySQL('1.1.1.3',3302)
    print(obj1)
    print(obj2)
    print(obj3)
    # print(obj4)
    '''
    # 单例模式实现方式二:
    '''
    import settings
    def singleton(cls):
        _instance=cls(settings.IP,settings.PORT)
        def wrapper(*args,**kwargs):
            if len(args) !=0 or len(kwargs) !=0:
                obj=cls(*args,**kwargs)
                return obj
            return _instance
        return wrapper
    @singleton #MySQL=singleton(MySQL) #MySQL=wrapper
    class MySQL:
        def __init__(self, ip, port):
            self.ip = ip
            self.port = port
    # obj=MySQL('1.1.1.1',3306) #obj=wrapper('1.1.1.1',3306)
    # print(obj.__dict__)
    obj1=MySQL() #wrapper()
    obj2=MySQL() #wrapper()
    obj3=MySQL() #wrapper()
    obj4=MySQL('1.1.1.3',3302) #wrapper('1.1.1.3',3302)
    print(obj1)
    print(obj2)
    print(obj3)
    print(obj4)
    '''
    # 单例模式实现方式三:
    '''
    import settings
    class Mymeta(type):
        def __init__(self,class_name,class_bases,class_dic):
            #self=MySQL这个类
            self.__instance=self(settings.IP,settings.PORT)
        def __call__(self, *args, **kwargs):
            # self=MySQL这个类
            if len(args) != 0 or len(kwargs) != 0:
                obj=self.__new__(self)
                self.__init__(obj,*args, **kwargs)
                return obj
            else:
                return self.__instance
    class MySQL(metaclass=Mymeta): #MySQL=Mymeta(...)
        def __init__(self, ip, port):
            self.ip = ip
            self.port = port

    obj1=MySQL()
    obj2=MySQL()
    obj3=MySQL()
    obj4=MySQL('1.1.1.3',3302)
    print(obj1)
    print(obj2)
    print(obj3)
    print(obj4)
    '''
    # 单例模式实现方式四:
    def f1():
        from singleton import instance
        print(instance)
    def f2():
        from singleton import instance,My
        SQL
        print(instance)
        obj=MySQL('1.1.1.3',3302)
        print(obj)
    f1()
    f2()
  • 相关阅读:
    8月面试题目收录
    html5读取本地文件,图片预览
    Identity Server4资料
    vue与Element实际应用参考
    webpack与vue环境搭建(转载)
    .NET使用Bogus生成大量随机数据(转载)
    Docker笔记:常用服务安装——Nginx、MySql、Redis(转载)
    RabbitMQ操作代码封装
    RSA加密与解密
    .NET CORE编写控制台程序应有的优雅姿势(转载)
  • 原文地址:https://www.cnblogs.com/3sss-ss-s/p/9550071.html
Copyright © 2011-2022 走看看