#装饰器实现单例模式def singleton1(func):    instance={}    def inner(*args,**kwargs):        if func not in instance:           instance[func]=func(*args,**kwargs)        return instance[func]    return inner@singleton1class user():    passfoo1=user()foo2=user()print(foo1 is foo2)

#使用修改基类实现单例模式class Singleton2():    def __new__(cls, *args, **kwargs):        if not hasattr(cls, '_instance'):            cls._instance = super().__new__(cls, *args, **kwargs)        return cls._instanceclass Foo(Singleton2):    passfoo3 = Foo()foo4 = Foo()print( foo3 is foo4)

#使用类实现单例模式，配合多线程import threadingimport timeclass Singleton(object):    _lock=threading.Lock()    def __init__(self):        time.sleep(1)    @classmethod    def instance(cls, *args, **kwargs):        if not hasattr(Singleton, "_instance"):            with Singleton._lock:                if not hasattr(Singleton, "_instance"):                    Singleton._instance = Singleton(*args, **kwargs)        return Singleton._instancedef task(arg):    obj = Singleton.instance()    print(obj)for i in range(10):    t = threading.Thread(target=task,args=[i,])    t.start()time.sleep(20)obj=Singleton.instance()print(obj)

#使用元类实现单例模式class SingletonType(type):    _instance_lock = threading.Lock()    def __call__(cls, *args, **kwargs):        if not hasattr(cls, "_instance"):            with SingletonType._instance_lock:                if not hasattr(cls, "_instance"):                    cls._instance = super(SingletonType,cls).__call__(*args, **kwargs)        return cls._instanceclass Foo(metaclass=SingletonType):    def __init__(self,name):        self.name = nameobj1 = Foo('name')obj2 = Foo('name')print(obj1 is obj2)