python StopIteration异常的使用

class MyNumbers:

    def __iter__(self):

        self.a = 1

        return self

    def __next__(self):

        if self.x < 20:

            x = self.a

            self.a += 1

            return x

        else:

            raise StopIteration

myclass = MyNumbers()

myiter = iter(myclass)

for x in myiter:

    print(x)