单例的实现

仅仅实现单利如下：
class single(object):
    __instance = None
    def __init__(self,name):
        self.name = name
  
    def __new__(cls, *args, **kwargs):
        if cls.__instance is None:
            cls.__instance = object.__new__(cls)
            return cls.__instance
        return cls.__instance

A1=single('aa')
print(id(A1))
print(A1.name)
A2=single('bb')
print(id(A2))
print(A2.name)

实现单例且只初始化化一次
class single(object):
    __instance = None
    __flag=None
    def __init__(self,name):
        if self.__flag is None:
            self.name = name
            self.__flag = True

    def __new__(cls, *args, **kwargs):
        if cls.__instance is None:
            cls.__instance = object.__new__(cls)
            return cls.__instance
        return cls.__instance
A1=single('aa')
print(id(A1))
print(A1.name)
A2=single('bb')
print(id(A2))
print(A2.name)

运行结果如下图：