Python__计算器

#Author wangmengzhu
import re
def cheng_and_chu(arg):
    val = arg[0]
    mch = re.search('d+.*d*[*/]+[+-]?d+.*d*', val)
    if not mch:
        return
    content = re.search('d+.*d*[*/]+[+-]?d+.*d*', val).group()
    if len(content.split('*'))>1:
        n1,n2 = content.split('*')
        value = float(n1) * float(n2)
    else:
        n1,n2 = content.split('/')
        value = float(n1) / float(n2)
    qianzhui,houzhui = re.split('d+.*d*[*/]+[+-]?d+.*d*', val, 1)
    new_str = "%s%s%s"%(qianzhui,value,houzhui)
    arg[0] = new_str
    cheng_and_chu(arg)

def jia_and_jian(arg):
    while True:
        if arg[0].__contains__('+-') or arg[0].__contains__("++") or arg[0].__contains__('-+') or arg[0].__contains__("--"):
            arg[0] = arg[0].replace('+-','-')
            arg[0] = arg[0].replace('++','+')
            arg[0] = arg[0].replace('-+','-')
            arg[0] = arg[0].replace('--','+')
        else:
            break
    if arg[0].startswith('-'):
        arg[1] += 1
        arg[0] = arg[0].replace('-','&')
        arg[0] = arg[0].replace('+','-')
        arg[0] = arg[0].replace('&','+')
        arg[0] = arg[0][1:]
    val = arg[0]
    mch = re.search('d+.*d*[+-]{1}d+.*d*', val)
    if not mch:
        return
    content = re.search('d+.*d*[+-]{1}d+.*d*', val).group()
    if len(content.split('+'))>1:
        n1, n2 = content.split('+')
        value = float(n1) + float(n2)
    else:
        n1, n2 = content.split('-')
        value = float(n1) - float(n2)
    before, after = re.split('d+.*d*[+-]{1}d+.*d*', val, 1)
    new_str = "%s%s%s" % (before,value,after)
    arg[0] = new_str
    jia_and_jian(arg)

def cal(sr):
    new_sr = [sr.strip('()'),0]
    cheng_and_chu(new_sr)
    jia_and_jian(new_sr)
    res = float(new_sr[0])
    return res

def basket(sr):
    flag = True
    while flag:
        m = re.search("([^()]+)",sr)
        if m:
            sub_sr = m.group()
            sub_res = cal(sub_sr)
            sr = sr.replace(m.group(),str(sub_res))
        else:
            print('结果：',cal(sr))
            flag = False

if __name__ == "__main__":
    print("----------欢迎使用计算器----------")
    while True:
        flag = True
        sr = input("输入要计算的函数(q:退出)：")
        sr = re.sub("s*","",sr)
        error = re.search('[0-9*/-+]',sr)
        while flag:
            if not error:
                print("输入有误")
                sr = input("请重新输入要计算的函数(q:退出)：")
            else:
                if error.group() == 'q':
                    exit("感谢使用，再见")
                basket(sr)
                flag = False