def str2float(s):
    s = s.split('.')
    def str2num(t):
        digits = {'0': 0, '1': 1, '2': 2, '3': 3, '4': 4, '5': 5, '6': 6, '7': 7, '8': 8, '9': 9}
        return digits[t]
    #小数点前
    def str2floatfront(x, y):
        return x * 10 + y
    #小数点后
    def str2floatback(x, y):
        return x * 0.1 + y
    front = reduce(str2floatfront, map(str2num, s[0]))
    back = 0.1 * reduce(str2floatback, map(str2num, s[1][::-1]))
    return front + back