python单例模式是什么意思

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._instance

import threading

daf task(arg):

  obj=Sigletion.instance()

  print(obj)

for i in range(10):

  t=threading.Thread(target=task,args=[i,])

  t.start()

import time

import threading

class 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._instance

obj1=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()

# 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 threading

class 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._instance

class Foo(metaclass=SingletonType):

  def __init__(self,name):

    self.name=name

obj1 = Foo('name')

obj2 = Foo('name')

print(obj1,obj2)