python3 运用正则实现计算器

import re

bracket = re.compile(r‘\([^()]+\)‘) # 寻找最内层括号规则
mul = re.compile(r‘(\d+\.?\d*\*-\d+\.?\d*)|(\d+\.?\d*\*\d+\.?\d*)‘)  # 寻找乘法运算规则
div = re.compile(r‘(\d+\.?\d*/-\d+\.?\d*)|(\d+\.?\d*/\d+\.?\d*)‘)  # 寻找除法运算规则
add = re.compile(r‘(-?\d+\.?\d*\+-\d+\.?\d*)|(-?\d+\.?\d*\+\d+\.?\d*)‘)  # 寻找加法运算规则
sub = re.compile(r‘(-?\d+\.?\d*--\d+\.?\d*)|(-?\d+\.?\d*-\d+\.?\d*)‘)  # 寻找减法运算规则
c_f = re.compile(r‘\([^*/]\)‘)  # 检查括号内是否运算完毕规则
strip = re.compile(r‘[^(].*[^)]‘)  # 脱括号规则
n_md = re.compile(‘\([^*/]+\)‘)
res = re.compile(‘([+-]?\d+\.?\d*)‘)
ills= re.compile(r‘[^0-9*/+\-\(\)]‘)
def Mul(exp):
    result = re.split(r‘\*‘,mul.search(exp).group())
    return exp.replace(mul.search(exp).group(),str(float(result[0])*float(result[1])))

def Div(exp):
    result = re.split(r‘/‘, div.search(exp).group())
    return exp.replace(div.search(exp).group(), str(float(result[0])/ float(result[1])))

def Add_Sub(exp):
    exp = exp.replace(‘++‘,‘+‘)
    exp = exp.replace(‘+-‘,‘-‘)
    exp = exp.replace(‘--‘,‘+‘)
    exp = exp.replace(‘-+‘,‘-‘)
    # print(exp)
    nums = re.findall(‘[+\-]?\d+\.?\d*‘,exp)
    count = 0
    for num in nums:
        count += float(num)
    return str(count)

# 没有添加用户输入判断
def calculator():
    while True:
        exp = input(‘>>>‘)
        if exp.strip().upper() == ‘Q‘:
            print(‘退出程序‘)
            exit()
        else:
            exp = exp.replace(‘ ‘,‘‘)
            if ills.search(exp):
                print(‘有非法字符!‘)
            else:
                while bracket.search(exp):
                    result = bracket.search(exp).group()
                    print(result)
                    if div.search(result):
                        exp = exp.replace(result,Div(result))
                    elif mul.search(result):
                        exp = exp.replace(result,Mul(result))
                    elif n_md.search(result):
                        exp = exp.replace(n_md.search(result).group(),Add_Sub(result))
                        print(exp)

                while True:
                    if div.search(exp):
                        result = div.search(exp).group()
                        exp = exp.replace(result,Div(result))
                    elif mul.search(exp):
                        result = mul.search(exp).group()
                        exp = exp.replace(result,Mul(result))
                    else:
                        result = Add_Sub(exp)
                        print(‘The answer is: %.2f‘%float(result))
                        break
calculator()
# print(1-2*((60-30+(-40/-5+20/4+3*4*5/2)*(9-2*5/3+7/3*99/4*2998+10*568/14))-(-4*3)/(16-3*2))-99*2)
# print(69*(69+1)*100+2*8)

原文地址：https://www.cnblogs.com/kuraki/p/9797248.html