python3简单实现支持括号的加减乘除运算

1.首先表达式的空格。

2.循环计算最内层带括号的表达式（提取运算符出现的顺序，然后计算）

3.计算最外层的表达式输出。

刚接触python，代码不够严谨，仅实现功能。不知道如何在函数中使用运算符变量做运算（使用的时候是字符串形式），希望知道的朋友告诉我，互相学习一下。

import re,math
def qcysf(s):
    while re.findall('\+\-|\+\+|\-\-|\-\+',s):
        s = s.replace('+-','-')
        s = s.replace('++','+')
        s = s.replace('--','+')
        s = s.replace('-+','-')
    return s
def yunsuan(a1):
    temp1 = re.sub('\d|\.|\+|-| ','',a1)
    # print(temp1)
    # print(a1)
    for i in temp1:
        if i == "*":
            b = re.search('(-?\d+\.?\d*\*-?\d+\.?\d*)', a1).group()
            # print(b)
            temp2 = round(float(b.split('*')[0]) * float(b.split('*')[1]),10)
            temp2 = '+' + str(temp2)
            a1 = a1.replace(b, temp2,1)
            # print(a1)
        else:
            b = re.search('(-?\d+\.?\d*/-?\d+\.?\d*)', a1).group()
            # print(b)
            temp2 = round(float(b.split('/')[0]) / float(b.split('/')[1]),10)
            temp2 = '+' + str(temp2)
            a1 = a1.replace(b, temp2,1)
            # print(a1)
    a1 = qcysf(a1)
    # print(a1)
    a2 = a1.lstrip('-')
    temp3 = re.sub('\d|\.| ', '', a2)
    for i in temp3:
        if i == "+":
                b = re.search('(-?\d+\.?\d*\+\d+\.?\d*)', a1).group()
                temp2 = round(float(b.split('+')[0]) + float(b.split('+')[1]),10)
                a1 = a1.replace(b, str(temp2),1)
                # print(a1)
        else:
            b = re.search('(\d+\.?\d*\-\d+\.?\d*)', a1).group()
            temp2 = round(float(b.split('-')[0]) - float(b.split('-')[1]),10)
            a1 = a1.replace(b, str(temp2),1)
            # print(a1)
    return a1

if __name__ == "__main__":
    a = input('请输入你要计算的内容：')
    a = a.replace(' ','')
    # print(a)
    if re.findall('[a-zA-Z]]',a):
        print('你输入的内容不合法')
    else:
        while re.search("\([^()]+\)", a):
            b = re.search("\([^()]+\)", a).group()
            # b = qcysf(b)
            # print(a)
            # print(b)
            b1 = re.sub('\(|\)','',b)
            # print(a)
            temp = yunsuan(b1)
            a = a.replace(b, str(temp))
        # print('这是倒数第二个',a)
        a = qcysf(a)
        a = yunsuan(a)
        print(a)

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