为什么 __iter__ 返回 self ？

如何解决为什么 __iter__ 返回 self ？

iter 所做的就是返回自我。这如何将类（PowTwo）的实例（数字）变成可迭代的？

class PowTwo:

def __init__(self,max=0):
    self.max = max

def __iter__(self):
    self.n = 0
    return self

def __next__(self):
    if self.n <= self.max:
        result = 2 ** self.n
        self.n += 1
        return result
    else:
        raise stopiteration


numbers = PowTwo(3)

i = iter(numbers)

print(next(i))
print(next(i))
print(next(i))
print(next(i))
print(next(i))