Python写的计算器程序（主要目的在于熟悉下正则表达式）

import re
s = '1-2*((60-30-(-40/5)*(9-2*5/3-7/3*99/4*2998-10*568/14.3))+(-4*3)/16-3)'
s2 = 1-2*((60-30-(-40/5)*(9-2*5/3-7/3*99/4*2998-10*568/14.3))+(-4*3)/16-3)
def check(s):#字符检错，不合法就返回False
    flag = True
    s = re.sub(' ','',s)#去空格
    if re.findall('[^\d+\-*/.()]',s):#检测出常规计算字符外的其他字符
        print('存在非法字符')
        flag = False
    elif re.findall('(\.\d\.)|(\D\.\D)|(\d\.\D)|(\D\.\d)',s):#检查出错误的小数
        print('存在小数格式异常')
        flag = False
    elif re.findall('[*/+\-]+[*/+\-]+|.[*/+\-]\)',s):#判断计算符号输入是否异常
        print('计算符号有误')
        flag = False
    if flag == False:
        s = None
    return s

def jisuan1(string):
    if re.findall('[()]',string):#有括号的处理方式
        string = re.sub('[()]','',string)
    while True:
        string.replace('+-','-')
        string.replace('-+', '-')
        string.replace('--', '+')
        try:
            x = re.search('[\-]*(?:\d+\.\d*|\d*)[*/](?:\d+\.\d*|\d*)',string).group()
            if '*' in x:
                y = float(x[:x.index('*')]) * float(x[x.index('*')+1:])
                string = string.replace(x,str(y))
            else:
                y = float(x[:x.index('/')]) / float(x[x.index('/') + 1:])
                string = string.replace(x, str(y))
        except :
            try:
                x = re.search('[\-]*(?:\d+\.\d*|\d+)[+\-](?:\d+\.\d*|\d+)', string).group()
                if '+' in x:
                    y = float(x[:x.index('+')]) + float(x[x.index('+') + 1:])
                    string = string.replace(x, str(y))
                else:
                    if x.count('-') >1:
                        y = float(''.join(['-',x.split('-')[1]])) + float(''.join(['-',x.split('-')[2]]))
                        string = string.replace(x, str(y))
                    else:
                        y = float(x[:x.index('-')]) - float(x[x.index('-') + 1:])
                        string = string.replace(x, str(y))
            except Exception as e:
                raise e
        if re.findall('[\-]*(?:\d+\.\d*|\d+)[+\-*/](?:\d+\.\d*|\d+)',string) == []:
            break
    return string

def jisuan2(s):#获取括号里的内容，并加以计算
    if s != None:
        while True:
            k = re.findall('(?:\d+\.\d*|\d+)[*/][\-+]+(?:\d+\.\d*|\d+)',s)
            for j in k:
                if '+' in j:
                    s = s.replace(j,j.replace('+',''))
                else:
                    s = s.replace(j, ''.join(['-', j.replace('-', '')]))
            s = s.replace('--', '+')
            s = s.replace('+-', '-')
            s = s.replace('-+', '-')
            try:
                x = re.search('\([^()]+\)',s).group()#得到最里层括号的内容
                a = jisuan1(x)  # 将内容计算出来
                s = s.replace(x, a)  # 将计算结果与之前的内容置换
            except Exception as e:
                a = jisuan1(s)  # 将内容计算出来
                s = a  # 将计算结果与之前的内容置换
            if re.findall('[\-]*(?:\d+\.\d*|\d+)[+\-*/](?:\d+\.\d*|\d+)', s) == []:
                break
    return s
#
a = check(s)
print('代码结果：',jisuan2(a))
print('正确结果：',s2)