【问答题任选2题作答】 请列出使用python实现

#1.如果有实例则返回，没有则创建实例
class Singleton(object):
    def __new__(cls, *args, **kw):
        if not hasattr(cls, '_instance'):
            orig = super(Singleton, cls)  
            cls._instance = orig.__new__(cls, *args, **kw)
        return cls._instance

#2.将所有实例的__dirt__都指向同一个字典
class Borg(object):
    _state = {}
    def __new__(cls, *args, **kw):
        ob = super(Borg, cls).__new__(cls, *args, **kw)
        ob.__dict__ = cls._state
        return ob
    
#3. 利用装饰器修饰类
def singleton(cls):
    instances = {}
    def getinstance(*args, **kw):
        if cls not in instances:
            instances[cls] = cls(*args, **kw)
        return instances[cls]
    return getinstance

@singleton
class xxxx:
    
#4 import
class My_Singleton(object):
    def foo(self):
        pass
my_singleton = My_Singleton()


from mysingleton import my_singleton
my_singleton.foo()
    

	#coding:utf8



	u'''



	实现单例模式



	author:renyi



	date:2018-09-19



	'''



	class Single(object):



	    __instance=None



	    def__init__(self):



	       pass



	    def__new__(cls):



	       if cls.__instance == None:



	           cls.__instance = object.__new__(cls)



	           return cls.__instance



	else:



	           return cls.__instance



	a=Single()



	print id(a)



	 



	b=Single()



	print id(b)