初学re模块--简易计算器

import re
import time
print("请输入需要计算的公式：")
source = input()
t1=time.time()
# source='6+7/(5-4*3/2+23)'
def check(s):
 flag = True
 if re.search('[a-z]', s):
 flag = False
 if re.search('[A-Z]', s):
 flag = False
 if re.search('\.{2,}', s):
 flag = False
 if re.search('\*{2,}', s):
 flag = False
 if re.search('\+{2,}', s):
 flag = False
 if re.search('-{2,}', s):
 flag = False
 if s.count('(')!= s.count(')'):
 flag = False
 return flag

def fmat(s):
 s=s.replace(' ', '')
 s=s.replace('++','+')
 s=s.replace('+-','-')
 s=s.replace('-+','-')
 return s

def mul(s):
 s1=re.search('\d+\.?\d*\*-?\d+\.?\d*',s).group()
 s2=re.split('\*',s1)
 s=s.replace(s1,str(float(s2[0])*float(s2[1])))
 return s

def div(s):
 s1=re.search('\d+\.?\d*/-?\d+\.?\d*',s).group()
 s2=re.split('/',s1)
 s=s.replace(s1,str(float(s2[0])/float(s2[1])))
 return s

def add(s):
 if s[0]=='-':
 s1=re.match('-\d+\.?\d*\+\d+\.?\d*',s).group()
 s2=re.split('-',s1)
 s3=re.split('\+',s2[1])
 s=s.replace(s1,str(float(s3[1])-float(s3[0])))
 else:
 s1 = re.match('\d+\.?\d*\+\d+\.?\d*', s).group()
 s3 = re.split('\+', s1)
 s = s.replace(s, str(float(s3[1])+float(s3[0])))
 return s

def sub(s):
 if s[0]=='-':
 s1=re.match('-\d+\.?\d*-\d+\.?\d*',s).group()
 s2=s1[1:-1]
 s3=re.split('-',s2)
 s=s.replace(s1,str(-float(s3[1])-float(s3[0])))
 else:
 s1 = re.match('\d+\.?\d*-\d+\.?\d*', s).group()
 s3 = re.split('-', s1)
 s = s.replace(s1,str(float(s3[0])-float(s3[1])))
 return s

def remove_paranthesis(s):
 s1=re.split('\(',s)
 s2=re.split('\)',s1[1])
 return s2[0]

if check(source):
 source = fmat(source)#格式化输出
 ret=source
 while ret.count('(') > 0:#有括号
 ret0= re.search('\([^()]+\)', ret).group()#判断最内层括号
 ret1=ret0
 while '*'in ret1 :#判断乘除法
 ret1=mul(ret1)
 while '/'in ret1:
 ret1=div(ret1)
 else:
 ret1=fmat(ret1)
 ret1 = ret1.replace(ret1, remove_paranthesis(ret1))
 while '+'in ret1 or '-'in ret1:
 ret2=re.search('\d+\.?\d*[+\-]\d+\.?\d*',ret1).group()
 if '+'in ret2:
 ret1=add(ret1)
 if '-'in ret2:
 ret1=sub(ret1)
 else:
 ret=ret.replace(ret0,ret1)
 else:
 while '*'in ret:#判断乘除法
 ret=mul(ret)
 while '/'in ret:
 ret=div(ret)
 else:
 ret=fmat(ret)
 while '+'in ret or '-'in ret:
 ret2=re.search('\d+\.?\d*[+\-]\d+\.?\d*',ret).group()
 if '+'in ret2:
 ret=add(ret)
 if '-'in ret2:
 ret=sub(ret)
 else:
 print(ret)
 print(time.time()-t1)