TypeError: iter() returned non-iterator of type 'int'

装的是python3.9的解释器, 在写python迭代器时报错TypeError: iter() returned non-iterator of type 'int'

class Gen(object):
    def __iter__(self):
        self.a=10
        return self.a  #此处应该直接返回self

    def __next__(self):
        self.a += 1
        return self.a

if __name__ == '__main__':
    g = Gen()
    gen = iter(g)
    print(g)
    print(next(gen))
    print(next(gen))
    print(next(gen))
    print(next(gen))

原来是__iter__方法中返回值错误，应该返回self，而不应该是self.a

    def __iter__(self):
        self.a=10
        return self

运行结果如下:

<__main__.Gen object at 0x0157E328>
11
12
13
14