def str2float(s):
    def char2num(s):
         digitals = {'0':0, '1':1, '2':2, '3':3, '4':4, '5':5, '6':6, '7':7, '8':8, '9':9}
         return digitals[s] 
    
    index = s.index('.')
    s1 = s[:index]
    s2 = s[index+1:]
    f = lambda x,y: x*10+y
    return reduce(f,map(char2num, s1)) + reduce(f,map(char2num, s2))/(10**len(s2))