一、單例模式

    a、單例模式分為四種：文件，類，基于__new__方法實現(xiàn)單例模式，基于metaclass方式實現(xiàn)

    b、類實現(xiàn)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__方法實現(xiàn)單例模式

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方式實現(xiàn)單例模式

"""
1.對象是類創(chuàng)建，創(chuàng)建對象時候類的__init__方法自動執(zhí)行，對象()執(zhí)行類的 __call__ 方法
2.類是type創(chuàng)建，創(chuàng)建類時候type的__init__方法自動執(zhí)行，類() 執(zhí)行type的 __call__方法(類的__new__方法,類的__init__方法)

# 第0步: 執(zhí)行type的 __init__ 方法【類是type的對象】class Foo:  def __init__(self):    pass  def __call__(self, *args, **kwargs):    pass# 第1步: 執(zhí)行type的 __call__ 方法#    1.1 調(diào)用 Foo類（是type的對象）的 __new__方法，用于創(chuàng)建對象。#    1.2 調(diào)用 Foo類（是type的對象）的 __init__方法，用于對對象初始化。obj = Foo()# 第2步：執(zhí)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)