一、单例模式

a、单例模式分为四种：文件，类，基于__new__方法实现单例模式，基于metaclass方式实现

b、类实现如下：

class Sigletion(objects): import time def __init__(self): time.sleep(1) @classmethod def instance(cls,*args,**kwargs) if not hasattr(Sigletion,'_instance'): Sigletion._instance=Sigletion(*args,**kwargs) return Sigletion._instanceimport threadingdaf task(arg): obj=Sigletion.instance() print(obj)for i in range(10): t=threading.Thread(target=task,args=[i,]) t.start()

c、基于__new__方法实现单例模式

import timeimport threadingclass Singleton(object): _instance_lock=threading.Lock() def __init__(self): pass def __new__(cls, *args, **kwargs): if not hasattr(Singleton,"_instance"): with Singleton._instance_lock: if not hasattr(Singleton,"_instance"): Singleton._instance=object.__new__(cls,*args,**kwargs) return Singleton._instanceobj1=Singleton()obj2=Singleton()print(obj1,obj2)def task(arg): obj = Singleton() print(obj)for i in range(10): t = threading.Thread(target=task,args=[i,]) t.start()

d、基于metaclass方式实现单例模式

"""
1.对象是类创建，创建对象时候类的__init__方法自动执行，对象()执行类的 __call__ 方法
2.类是type创建，创建类时候type的__init__方法自动执行，类() 执行type的 __call__方法(类的__new__方法,类的__init__方法)

# 第0步: 执行type的 __init__ 方法【类是type的对象】class Foo: def __init__(self): pass def __call__(self, *args, **kwargs): pass# 第1步: 执行type的 __call__ 方法# 1.1 调用 Foo类（是type的对象）的 __new__方法，用于创建对象。# 1.2 调用 Foo类（是type的对象）的 __init__方法，用于对对象初始化。obj = Foo()# 第2步：执行Foodef __call__ 方法obj()"""import threadingclass SingletonType(type): _instace_lock=threading.Lock() def __call__(cls, *args, **kwargs): if not hasattr(cls, "_instance"): with SingletonType._instace_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,obj2)