class Foo:
    instance = None
    def __init__(self,name):
        self.name = name

    @classmethod    #类方法
    def get_instance(cls):  #cls类名
        if cls.instance:
            return cls.instance
        else:
            obj=cls(‘alex‘)
            cls.instance = obj
            return obj

obj1 = Foo.get_instance()
print(obj1)
obj2 = Foo.get_instance()
print(obj2)