python 函数嵌套时出现的参数调用wen't

Question

def str2float(s):
    flag = 0
    g = 1.0
    DIGITS = {'0': 0, '1': 1, '2': 2, '3': 3, '4': 4, '5': 5, '6': 6, '7': 7, '8': 8, '9': 9, '.': 10}

    def fn(x, y):
        print(g)
        if y != 10 and flag == 0:
            return x * 10 + y
        elif y == 10 and flag == 0:
            flag = 1
            return x
        else:
            g = g * 0.1
            print(g)
            return x + y * g

    def char2num(s):
        return DIGITS[s]

    return reduce(fn, map(char2num, s))

题目要求：利用map和reduce编写一个str2float函数，把字符串'123.456'转换成浮点数123.456：
其中g和flag两个参数显示未定义但DIGITS却可以正常调用请问为什么。

Answer 1

https://segmentfault.com/q/1010000020450098/