迭代器iter用法

class Counter(object):
    def __init__(self):
        self.i = [1,2,3,4,5,6]
        self.n = iter(self.i)
    def __call__(self):
        x = next(self.n)
        print('call',x)
        return x
it = Counter()
t1 = iter(it, 5) # it必须是callable的，否则无法返回callable_iterator
for v in t1:
    print(v)
# 结果
call 1
1
call 2
2
call 3
3
call 4
4
call 5