创建单例模式的六种方式

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

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

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。