Python使用正则实现计算字符串算式

s = '1+2*(6/2-9+3*(3*9-9))'
print(eval(s))
#97.0

import re
pattern = re.compile(r'\([^(^)]*?\)')
s = '1+2*(6/2-9+3*(3*9-9))+(6-3)'
ret = pattern.findall(s)
print(ret)
#['(3*9-9)','(6-3)']

ret2 = []
pattern2 = re.compile(r'\((?P<tag>.*?)\)')
for i in range(len(ret)):
 ret3 = pattern2.search(ret[i])
 ret2.append(ret3.group('tag'))
print(ret2)
#['3*9-9', '6-3']

def mul_div(s):
 if '*' in s:
 s = s.split('*')
 return float(s[0]) * float(s[1])
 elif '/' in s:
 s = s.split('/')
 return float(s[0]) / float(s[1])
while True:
 pattern3 = re.compile(r'[-+*/]?(?P<tag>-?\d+(\.\d+)?[*/]-?\d+(\.\d+)?)')
 ret3 = pattern3.search(ret2[1])
 try:
 ret4 = ret3.group('tag')
 except Exception as e:
 pass
 if '*' not in ret2[1] and '/' not in ret2[1]:
 break 
 else:
 ret2[1] = ret2[1].replace(ret4, str(mul_div(ret4)))

def add_sub(s):
 if '+' in s:
 s = s.split('+')
 return float(s[0]) + float(s[1])
 else:
 if s[0] == '-':
  s = s[1::].split('-', 1)
  s[0] = '-' + s[0]
  return float(s[0]) - float(s[1])
 else:
  s = s.split('-', 1)
  return float(s[0]) - float(s[1])
while True:
 pattern3 = re.compile(r'-?\d+(\.\d+)?[-+]-?\d+(\.\d+)?')
 ret3 = pattern3.search(ret2[i])
 try:
 ret4 = ret3.group()
 except Exception as e:
 pass
 if '+' not in ret2[i] and '-' not in ret2[i][1::]:
 break
 else:
 ret2[i] = ret2[i].replace(ret4, str(add_sub(ret4)))

def str_replace(lst1,lst2):
 for i in range(len(lst1)):
 global str1
 str1 = str1.replace(lst1[i], lst2[i])
 
str_replace(ret1,ret2)

str1 = '1+2*(6/2-9+3*(3*9-9))'
str1 = '( )'.replace(' ',str1)

#!/usr/bin/env python
# -*- coding:utf-8 -*-
import re
# 乘除法
def mul_div(s):
 if '*' in s:
 s = s.split('*')
 return float(s[0]) * float(s[1])
 elif '/' in s:
 s = s.split('/')
 return float(s[0]) / float(s[1])
# 加减法
def add_sub(s):
 if '+' in s:
 s = s.split('+')
 return float(s[0]) + float(s[1])
 else:
 if s[0] == '-':
  s = s[1::].split('-', 1)
  s[0] = '-' + s[0]
  return float(s[0]) - float(s[1])
 else:
  s = s.split('-', 1)
  return float(s[0]) - float(s[1])
# 替换字符串
def str_replace(lst1,lst2):
 for i in range(len(lst1)):
 global str1
 str1 = str1.replace(lst1[i], lst2[i])
# 匹配最内层括号
pattern1 = re.compile(r'\([^(^)]*?\)')
str1 = '1+2*(6/2-9+3*(3*9-9))'
str1 = '( )'.replace(' ',str1)
while True:
 if '(' not in str1 and ')' not in str1:
 break
 ret1 = pattern1.findall(str1)
 # 匹配括号内的内容
 ret2 = []
 pattern2 = re.compile(r'\((?P<tag>.*?)\)')
 for i in range(len(ret1)):
 ret = pattern2.search(ret1[i])
 ret2.append(ret.group('tag'))
 # 计算乘除法
 while True:
  pattern3 = re.compile(r'[-+*/]?(?P<tag>-?\d+(\.\d+)?[*/]-?\d+(\.\d+)?)')
  ret3 = pattern3.search(ret2[i])
  try:
  ret4 = ret3.group('tag')
  except Exception as e:
  pass
  if '*' not in ret2[i] and '/' not in ret2[i]:
  break
  else:
  ret2[i] = ret2[i].replace(ret4, str(mul_div(ret4)))
 # 计算加法
 while True:
  pattern3 = re.compile(r'-?\d+(\.\d+)?[-+]-?\d+(\.\d+)?')
  ret3 = pattern3.search(ret2[i])
  try:
  ret4 = ret3.group()
  except Exception as e:
  pass
  if '+' not in ret2[i] and '-' not in ret2[i][1::]:
  break
  else:
  ret2[i] = ret2[i].replace(ret4, str(add_sub(ret4)))
 str_replace(ret1,ret2)
print(str1)
#97.0