python 计算器

import re
def atom_cal(exp): # 计算乘除法
    if '*' in exp:
        a,b = exp.split('*')
        return str(float(a) * float(b))
    elif '/' in exp:
        a, b = exp.split('/')
        return str(float(a) / float(b))

def fuhaochuli(exp): # 符号处理
    exp = exp.replace('++','+')
    exp = exp.replace('-+','-')
    exp = exp.replace('+-','-')
    exp = exp.replace('--','+')
    return exp

def mul_div(exp): # 匹配乘除法进行计算并替换
    while True:
        ret = re.search('\d+(\.\d+)?[*/]-?\d+(\.\d+)?',exp)
        if ret:
            a = ret.group()
            b = atom_cal(a)
            exp = exp.replace(a,b)
        else:return exp

def add_sub(exp): # 匹配加减法计算并进行替换
    res = re.findall('[-+]?\d+(?:\.\d+)?',exp)
    exp_sum = 0
    for i in res:
        exp_sum += float(i)
    return exp_sum

def cal(exp):    # 计算
    exp = mul_div(exp)
    exp = fuhaochuli(exp)
    exp_sum = add_sub(exp)
    return exp_sum

def main(exp):    # 格式处理,计算结果并进行替换
    exp = exp.replace(" ",'')
    while True:
        ret = re.search('\([^()]+\)',exp)
        if ret:
            inner_bracket = ret.group()
            res = str(cal(inner_bracket))
            exp = exp.replace(inner_bracket,res)
            exp = fuhaochuli(exp)
        else:break
    return cal(exp)

s = '3*(1+3-0.62)'
ret = main(s)
print(ret)