Python中创建单例模式的六种方式

今天药忘吃喽~ 2022-09-11 12:15 113阅读 0赞

**一、基于装饰器实现单例模式**

#装饰器实现单例模式
    
    def singleTon(cls):
        def wrapper(*args,**kwargs):
            if not hasattr(cls,'_instance'):
                cls._instance = cls(*args,**kwargs)
            return cls._instance
        return wrapper
    
    @singleTon
    class SingleTonTest:
        pass
    
    s1 = SingleTonTest() 
    s2 = SingleTonTest() 
    print(s1) #<__main__.SingleTonTest object at 0x0000000000656860>
    print(s2) #<__main__.SingleTonTest object at 0x0000000000656860>

**二、基于元类实现单例模式**

class MyType(type):
    
        def __call__(self, *args, **kwargs):
            """ self指的是SingleTonTest类 :param args: :param kwargs: :return: """
            if not hasattr(self,'_instance'):
                self._instance = super(MyType,self).__call__(*args,**kwargs)
            return self._instance
    
    class SingleTonTest(metaclass=MyType):
        pass
    
    #SingleTonTest是元类MyType的对象，对象加括号执行元类中的__call__方法
    s1 = SingleTonTest()
    s2 = SingleTonTest()
    print(s1) #<__main__.SingleTonTest object at 0x0000000000646898>
    print(s2) #<__main__.SingleTonTest object at 0x0000000000646898>

**三、基于`__new__`方法实现单例模式**

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    class SingleTonTest:
    
        def __new__(cls, *args, **kwargs):
            """ cls：<class '__main__.SingleTonTest'> :param args: :param kwargs: :return: """
            if not hasattr(cls,'_instance'):
                cls._instance = super(SingleTonTest,cls).__new__(cls, *args, **kwargs)
            return cls._instance
    
    s1 = SingleTonTest()
    s2 = SingleTonTest()
    print(s1) #<__main__.SingleTonTest object at 0x0000000000BD68D0>
    print(s2) #<__main__.SingleTonTest object at 0x0000000000BD68D0>

**四、基于静态方法实现单例模式**

class SingleTonTest:
    
        @classmethod
        def getInstance(cls):
            if not hasattr(cls,'_instance'):
                cls._instance = cls()
            return cls._instance
    
    s1 = SingleTonTest.getInstance()
    s2 = SingleTonTest.getInstance()
    print(s1) #<__main__.SingleTonTest object at 0x0000000000646828>
    print(s2) #<__main__.SingleTonTest object at 0x0000000000646828>

**五、基于模块实现单例模式**

''' 学习中遇到问题没人解答？小编创建了一个Python学习交流QQ群：531509025 寻找有志同道合的小伙伴，互帮互助,群里还有不错的视频学习教程和PDF电子书！ '''
    class SingleTonTest:
        pass
    
    s = SingleTonTest()
    
    #在另一个py文件中导入该类对象
    from base import s
    
    print(s)

**六、Monostate单例模式**

将所有创建对象的`__dict__`属性指向同一个字典，这样所有的对象实现了数据的共享。

class Borg:
    
        __shared_state={ }
    
        def __new__(cls, *args, **kwargs):
            obj = super(Borg,cls).__new__(cls, *args, **kwargs)
            obj.__dict__ = cls.__shared_state
            return obj
    
    #共享同一个字典，一个对象改变属性，另一个也跟着改变
    b1 = Borg()
    b1.name = 'Bright'
    b2 = Borg()
    
    print(b1.__dict__) #{'name': 'Bright'}
    print(b2.__dict__) #{'name': 'Bright'}

将`_shared_state`变量作为一个中间变量，并且赋值给python中存储类所有对象状态的`__dict__`变量，这在实例后，会产生两个不同的对象，但是`b1.__dict__`和`b2.__dict__`都指向了`_shared_state`的内存地址。

注意，这种单例模式是数据的单例，对象还是两个不一样的对象。