from functools import reduce
def str2num(s):
    def char2num(c):#單個字元轉成int型別
        digits = {'0': 0, '1': 1, '2': 2, '3': 3, '4': 4, '5': 5, '6': 6, '7': 7,
                  '8': 8, '9': 9}
        return digits[c]

    def fn(x, y):
        return x * 10 + y

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

if
 
 __name__ == '__main__':
    print(str2num('1900'))

說明：
1.reduce(func, [x1, x2, x3])： 返回 func(func(x1, x2), x3)