python实现计算器功能

 import re

 def strip_operate(exp):    # 合并多余的操作符
     exp = exp.replace("+-", "-")
     exp = exp.replace("--", "+")
     return exp  

 def cal_exp_son(exp_son):    # 计算两数的乘除
     if "/" in exp_son:
         a, b = exp_son.split("/")
         return str(float(a)/float(b))
     elif "*" in exp_son:
         a, b = exp_son.split("*")
         return str(float(a)*float(b))

 def cal_no_bracket(exp):    # 计算一个里面已经没有括号的式子
     exp = exp.strip("()")
     while True:
         ret1 = re.search(r"\d+\.?\d*[/*]-?\d+\.?\d*", exp)
         if ret1:     # 先乘除
             exp_son = ret1.group()
             ret2 =cal_exp_son(exp_son)
             exp = exp.replace(exp_son, ret2)
             exp = strip_operate(exp)
         else:      # 后加减
             ret4 = re.findall(r"-?\d+\.?\d*", exp)
             sum1 = 0
             for i in ret4:
                 sum1 += float(i)
             return str(sum1)

 def main_1(express):
     while True:
         ret = re.search(r"\([^()]+\)", express)
         if ret:
             express_no_bracket = ret.group()
             ret3 = cal_no_bracket(express_no_bracket)
             express = express.replace(express_no_bracket, ret3)
             express = strip_operate(express)
         else:
             ret4 = cal_no_bracket(express)
             return ret4

 express = '1 - 2 * ( (60-30 +(-40/5) * (9-2*5/3 + 7 /3*99/4*2998 +10 * 568/14 )) - (-4*3)/ (16-3*2) )'
 express = express.replace(" ", "")
 ret5 = main_1(express)
 print(ret5)