Python如何用正则表达式实现计算器功能

import re

def son_deal(exp): #此处类似于8+-9——10++9 8+9+10-11
  if '--'or '+-' in exp:
    exp= exp.replace('--','+') #'1-2*60-30+-8.0.0-10.0.0+2.3.300000000000002e+4.74950.0+5680.0.0--12.0.0-6.0'
    exp= exp.replace('+-','-')
    return exp
def add_minus_func(exp):
  lst = re.findall('-?\d*\.?\d*', exp)
  sum = 0.0
  if len(lst)==0:
    sum=float(exp)
  else:
    new_lst = filter(None, lst)
    for l in new_lst:
      l = float(l)
      sum += l
  return str(sum)
def mul_div(exp):
  print('ab值前的表达式：%s'%exp)
  if '*' in exp:
    a,b=exp.split('*')
    return str(float(a)*float(b))
  if '/' in exp:
    a, b = exp.split('/')
    print('a的值是%s,b的值是%s'%(a,b))
    print ('除后的结果：',str(float(a)/float(b)))
    return str(float(a)/float(b))


def get_no_bracket_express(exp):
    exp=exp.strip('()')
    while 1:
      ret=re.search(r'\d*\.?\d*[*/]-?\d*\.?\d*',exp)
      if ret:
        old_express=ret.group()
        exp = exp.replace(old_express,mul_div(old_express))
        print('括号里计算的表达式 ',exp)
      else:
        exp=son_deal(exp)
        print('去掉+-，--后的结果',exp)
        exp=add_minus_func(exp)
        return exp

#找出括号，返回替换后的值
def search_bracket_exp(exp):
  regex = r'\([^()]+\)'
  while 1:
    ret= re.search(regex, exp)
    if ret:
      new_exp_c=ret.group()
      print(new_exp_c)
      exp = exp.replace(new_exp_c, get_no_bracket_express(new_exp_c))
      print('去掉括号的结果',exp)
    else:
      #1-2*-1388328.8880952382
      exp =get_no_bracket_express(exp)
      return exp

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