无法解包不可迭代的NoneType对象

Question

我需要编写2个内部函数f_current，f_counter。当前应该返回，输入值，而计数器必须返回递增值。

但是我下面的代码抛出错误“无法解压缩不可迭代的NoneType对象”。请帮忙。

import sys
import os



# Add the factory function implementation here
def factory(n):

    def current(n):
        return n

    def counter(n):
        n = n+1
        return self.n


    return

f_current, f_counter = factory(int(input()))


if __name__ == "__main__":
    with open(os.environ['OUTPUT_PATH'], 'w') as fout:
        func_lst = [f_current, f_counter]
        res_lst = list()
        for func in func_lst:
            res_lst.append(func())
        fout.write("{}\n{}".format(*res_lst))