Python 用正则表达式 写 简单的计算器

流程图：

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代码：

import re
def special_handles(formula):
    """ 操作加减符号处理
       :param expression:表达式
       :return:计算结果       """
    formula = formula.replace('+-','-')
    formula = formula.replace('--', '+')
    formula = formula.replace('-+', '-') 
    formula = formula.replace('++', '+')
    return formula
def calculate(formula):
    """ 操作加减乘除
       :param expression:表达式
       :return:计算结果       """
    formula = formula.strip('()')
    formula = special_handles(formula)
    signs = re.findall('[+-]',formula)
    melement = re.split('[+-]',formula)
    if melement[0] == '':
        melement[1]= '-%s'%melement[1] 
       del melement[0]
       del signs[0]
    for index,i in enumerate(melement):
        if i.endswith('*') or i.endswith('/'): 
           melement[index] = i + '-%s'%melement[index+1]
            del signs[index]
            del melement[index+1]
    for index,i in enumerate(melement):
        sub_res =mult_div(i)
        melement[index]=sub_res
    res2 = None
    for index,i in enumerate(melement): 
       if res2:
            if signs[index-1] == '+':
                res2 += float(i)
            elif signs[index-1] == '-':
                res2 -= float(i) 
       else: 
           res2 = float(i)
    return res2
def mult_div(formula):
    """ 操作乘除 
        :param expression:表达式
        :return:计算结果    """
    signs = re.findall('[*/]',formula)
    element = re.split('[*/]',formula)
    res = None
    for index, i in enumerate(element): 
       if res: 
           if signs[index-1] == '*':
                res *= float(i)
            elif signs[index-1] == '/':
                res /= float(i) 
       else:
         res = float(i) 
   return res
def calculator(formula):
    """ 操作计算简易公式 
         :param expression:表达式
         :return:计算结果       """
    formula = re.sub('\s+','',formula)
    final_outcome = None
    flag = False
    count = 1
    while not flag:
        brackets = re.search('\([^()]+\)', formula)
        if brackets:
            brackets_outcome = calculate(brackets.group())
            print('\033[41;1m第%d次\033[0m括号内\033[42;1m%s\033[0m计算结果:%d'%(count,brackets.group(),brackets_outcome))
            count += 1
            formula = formula.replace(brackets.group(),str(brackets_outcome)) 
       else: 
           final_outcome = calculate(formula)
            print('\n\n\033[42;1m最终结果:\033[0m%s'%final_outcome)
            flag = True
res = calculator("1 - 2 * ( (60-30 +(-9-2-5-2*3-5/3-40*4/2-3/5+6*3) * (-9-2-5-2*5/3 + 7 /3*99/4*2998 +10 * 568/14 )) - (-4*3)/ (16-3*2) )")

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