开发一个简单的python计算器

要求：

1. 实现加减乘除及拓号优先级解析
2. 用户输入 1 - 2 * ( (60-30 +(-40/5) * (9-2*5/3 + 7 /3*99/4*2998 +10 * 568/14 )) - (-4*3)/ (16-3*2) )等类似公式后，必须自己解析里面的(),+,-,*,/符号和公式(不能调用eval等类似功能偷懒实现)，运算后得出结果，结果必须与真实的计算器所得出的结果一致

 import re

 def main():

     a = ''.join(input('请输入需要计算的算式').split())

     while True:
         if '(' in a:
             ct = re.search(r'\(([^()]+)\)', a)
             if ct is not None:
                 b = ct.groups()[0]
                 c = count(b)
                 a = re.sub(r'\(([^()]+)\)', str(c), a, 1)
         else:
             c = count(a)
             print(c)
             break

 def add_min(a):
     '''
     计算加减法
     :param:
     :return:
     '''

     if '--' in a:
         a = a.replace('--', '+')

     c = re.findall(r'-?\d+\.?\d*', a)
     ls = []
     for i in c:
         ls.append(float(i))
     rest = sum(ls)
     return rest

 def mul(a):
     '''
     计算剩数
     :param ct:
     :return:
     '''

     b = re.search(r'\d+\.?\d*(\*-?\d+\.?\d*)+', a)
     if b is not None:
         b = b.group()
         rest = 1
         c = re.findall(r'-?\d+\.?\d*', b)
         ls =[]
         for item in c:
             ls.append(float(item))
         for i1 in range(len(ls)):
             rest = rest * ls[i1]
         a = re.sub(r'\d+\.?\d*(\*-?\d+\.?\d*)+', str(rest), a, 1)
         return a

 def div(a):
     '''
     计算出发
     :param a:
     :return:
     '''

     b = re.search(r'\d+\.?\d*(\/-?\d+\.?\d*)+', a)
     if b is not None:
         b = b.group()
         c = re.findall(r'-?\d+\.?\d*', b)
         ls =[]
         for i in c:
             ls.append(float(i))
         rest = ls[0]
         for i1 in range(1,len(ls)):
             rest = rest / ls[i1]
         a = re.sub(r'\d+\.?\d*(\/-?\d+\.?\d*)+', str(rest), a, 1)
         return a

 def count(b):
     '''
     计算结果
     :return:
     '''
     while True:
         if '*' in b:
             c = b.split('*')
             if '/' in c[0]:
                 b = div(b)
             else:
                 b = mul(b)
         elif '/' in b:
             b = div(b)

         elif '+' or '-' in b:
             b = add_min(b)
             return b
         else:
             return b

 main()