import re
import time
print("請輸入需要計算的公式：")
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)#格式化輸出
    ret=source
    while ret.count(‘(‘) > 0:#有括號
        ret0= re.search(‘\([^()]+\)‘, ret).group()#判斷最內層括號
        ret1=ret0
        while ‘*‘in ret1 :#判斷乘除法
            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:#判斷乘除法
            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)

初學re模塊--簡易計算器