Python中单例模式总结
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：
classSigletion(objects): importtime def__init__(self): time.sleep(1) @classmethod definstance(cls,*args,**kwargs) ifnothasattr(Sigletion,'_instance'): Sigletion._instance=Sigletion(*args,**kwargs) returnSigletion._instance importthreading daftask(arg): obj=Sigletion.instance() print(obj) foriinrange(10): t=threading.Thread(target=task,args=[i,]) t.start()
c、基于__new__方法实现单例模式
importtime importthreading classSingleton(object): _instance_lock=threading.Lock() def__init__(self): pass def__new__(cls,*args,**kwargs): ifnothasattr(Singleton,"_instance"): withSingleton._instance_lock: ifnothasattr(Singleton,"_instance"): Singleton._instance=object.__new__(cls,*args,**kwargs) returnSingleton._instance obj1=Singleton() obj2=Singleton() print(obj1,obj2) deftask(arg): obj=Singleton() print(obj) foriinrange(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】
classFoo:
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()
"""
importthreading
classSingletonType(type):
_instace_lock=threading.Lock()
def__call__(cls,*args,**kwargs):
ifnothasattr(cls,"_instance"):
withSingletonType._instace_lock:
ifnothasattr(cls,"_instance"):
cls._instance=super(SingletonType,cls).__call__(*args,**kwargs)
returncls._instance
classFoo(metaclass=SingletonType):
def__init__(self,name):
self.name=name
obj1=Foo('name')
obj2=Foo('name')
print(obj1,obj2)