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)