def str2float(s):

    DIGITS = {'0': 0, '1': 1, '2': 2, '3': 3, '4': 4, '5': 5, '6': 6, '7': 7, '8': 8, '9': 9,'.':'.'}  

    sList = s.split('.')

    def str2list(index):

        return DIGITS[index]

    def frontDotF(x,y):

        return x * 10 + y

    frontDot = list(map(str2list,sList[0]))

    behindDot = list(map(str2list,sList[1]))

    s1 = reduce(frontDotF,frontDot)

    s2 = reduce(frontDotF,behindDot)/10**len(behindDot)

    return s1 + s2