代码如下：

# -*- coding: utf-8 -*-

from functools import reduceDIGITS = {'0': 0, '1': 1, '2': 2, '3': 3, '4': 4, '5': 5, '6': 6, '7': 7, '8': 8, '9': 9}def str2float(s):    def char2num(s):        return DIGITS[s]    def fn(x, y):        return x * 10 + y    integer_str = s.split('.')[0]    decimal_str = s.split('.')[1]    integer_num = map(char2num, integer_str)    decimal_num = map(char2num, decimal_str)    # <class 'map'>    float_num = reduce(fn, integer_num) + reduce(fn, decimal_num) / pow(10, len(decimal_str))    return float_numprint('str2float(\'123.456\') =', str2float('123.456'))if abs(str2float('123.456') - 123.456) < 0.00001:    print('测试成功!')else:    print('测试失败!')