Python 70行代码实现简单算式计算器解析

import re
'''根据本逻辑，‘-'必须早于‘+'循环 否则特殊情况会报错
  原因是若出现符号--，会被处理为+，若+优先遍历，最后+将无法被处理'''
oper_char = ['^','*','/','-','+']
def format_str(s):
  '''除去空格和两边括号'''
  return s.replace(' ','').replace('(','').replace(')','')
 
def handle_symbol(s):
  '''处理多个运算符并列的情况'''
  return s.replace('+-','-').replace('--','+').replace('-+','-').replace('++','+')
 
def cal(x,y,opertor):
  '''加减乘除开方'''
  if opertor == '^':return x**y
  elif opertor == '*':return x*y
  elif opertor == '/':return x/y
  elif opertor == '+':return x+y
  elif opertor == '-':return x-y
 
def Bottom_operation(s):
  '''无括号运算 返回一个浮点数
    symbol用于判断返回值是正还是负'''
  symbol = 0
  s = handle_symbol(s)
  for c in oper_char:
    while c in s:
      id,char = (s.find(c),c)
      if c in ('*','/') and '*' in s and '/' in s:
        ids,idd = (s.find('*'),s.find('/'))
        id,char = (ids,'*') if ids <= idd else (idd,'/')
      if c in ('+','-') and '+' in s and '-' in s:
        ida,idd = (s.find('+'),s.find('-'))
        id,char = (ida,'+') if ida <= idd else (idd,'-')
      if id == -1:break
      left,right = ('','')
      for i in range(id - 1,-1,-1):
        if s[i] in oper_char:break
        left = s[i] + left
      for i in range(id + 1,len(s)):
       if s[id+1] == '-':
         right += s[i]
        continue
        if s[i] in oper_char:break
        right += s[i]
      if right == '' or left == '':
        if s[0] in ('-','+'):
          if '+' not in s[1:] and '-' not in s[1:]:break
          s = s[1:].replace('-','负').replace('+','-').replace('负','+')
          symbol += 1
          continue
        else:return '输入算式有误'
      old_str = left + char + right
      new_str = str(cal(float(left),float(right),char))
      s = handle_symbol(s.replace(old_str,new_str))
  return float(s) if symbol % 2 == 0 else -float(s)
 
def get_bottom(s):
  '''获取优先级最高的表达式'''
  res = re.search('\([^()]+\)',s)
  if res != None:return res.group()
 
if __name__ == '__main__':
  while True:
    s1 = input('请输入您要计算的表达式(支持加减乘除开方): ')
    while get_bottom(s1) != None:
      source = get_bottom(s1)
      result = Bottom_operation(format_str((source)))
      s1 = s1.replace(source,str(result))
    print(Bottom_operation(format_str(s1)))