python singleton 4种单例

概述def singleton(cls, *args, **kwargs): instances = {} def inner(cls, *args, **kwargs): if cls not in instances: instances[cls] = cls(*args, **kwargs) return instances

def singleton(cls,*args,**kwargs):    instances = {}    def inner(cls,**kwargs):        if cls not in instances:            instances[cls] = cls(*args,**kwargs)        return instances[cls]    return inner@singletonclass Test1:    pass# 推荐使用这种 简单好用 线程安全# ===========================================================import threadingclass Singleton:        def __init__(self,cls):        self.__cls = cls        self.__instance = None        self._lock = threading.Lock()    def __call__(self,**kwargs):        self._lock.acquire()        if self.__instance is None:            self.__instance = self.__cls(*args,**kwargs)        self._lock.release()        return self.__instance            @Singletonclass Test2:    pass# 继承时的执行顺序 base new -> son new -> son init. new 相当于构造方法，init相当于实例后再初始化 先执行父类的new 就好比先是人再是学生# ==============================================================class SingleBase(object):    instance = None        def __new__(cls,**kwargs):        # if not instance:        #     instance = cls.__new__(*args,**kwargs):        # return instance        if cls.instance is None:            cls.instance = object.__new__(cls)        return cls.instance    def __init__(self):        passclass Test3(SingleBase):        def __init__(self,name):        self._name = name    def get_name(self):        return self._name# Meta 这个我还不是很懂# =====================================================class MetaSingleton(type):    _instances = {}    def __call__(cls,**kwargs):        if cls not in cls._instances:            cls._instances[cls] = super().__call__(*args,**kwargs)        return cls._instances[cls]class Test4(Metaclass=MetaSingleton):        def __init__(self):        passif __name__ == '__main__':    t1 = Test3('jwang')    t2 = Test3('hello')    print(ID(t1))    print(ID(t2))    print(t1.get_name())    print(t2.get_name())    test3 = Test4()    test4 = Test4()    print(ID(test3) == ID(test4))

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