使用python实现计算器功能

学习python过程中的作业。实现了+、-、×、/、及幂运算，支持括号优先级。

代码为python3.5

 import re
 def formatEquation(string):
     string = string.replace("--", "+")
     string = string.replace("-+", "-")
     string = string.replace("++", "+")
     string = string.replace("+-", "-")
     string = string.replace("*+", "*")
     string = string.replace("/+", "/")
     string = string.replace(' ', '')
     return string
 def findErrorChar(equation):
     '''
     查找非计算的字符
     '''
     re_rule = r"[^ \.\d\+\-\*\/\(\)]+"
     req = re.findall(re_rule,equation)
     return req
 def findErrorOperator(equation):
     '''
     查找连续多次出现的运算符号
     '''
     re_rule = r'[+\-/*][+\-/*][+\-/*]*'
     req = re.findall(re_rule,equation)
     while '**' in req:
         req.remove('**')
     return req
 def addSubtract(equation):
     '''
     加减法运算，递归运算
     '''
     re_rule = r'[-]?\d+\.?\d*[+-]\d+\.?\d*'
     if re.search(re_rule,equation):
         req = re.search(re_rule,equation).group()
         if '+' in req:
             x,y = req.split('+')
             string = str(float(x) + float(y))
             equation = formatEquation(equation.replace(req,string))
             return addSubtract(equation)
         if '-' in req:
             if req.startswith('-'):
                 req1 = req[1:]
                 x,y = req1.split('-')
                 x = '-'+x
             else:
                 x,y = req.split('-')
             string = str(float(x) - float(y))
             equation = formatEquation(equation.replace(req,string))
             return addSubtract(equation)
     else:
         return equation

 def multiplicationDivision(equation):
     '''
     乘除法及幂运算，递归运算
     '''
     re_rule = r'\d+\.?\d*([*/]|\*\*)[\-]?\d+\.?\d*'
     print(11)
     if re.search(re_rule,equation):
         req = re.search(re_rule,equation).group()
         print(req)
         if '**' in req:
             x,y = req.split('**')
             string = str(float(x) ** float(y))
             equation = formatEquation(equation.replace(req,string))
             return multiplicationDivision(equation)
         if '*' in req:
             x,y = req.split('*')
             string = str(float(x) * float(y))
             equation = formatEquation(equation.replace(req,string))
             return multiplicationDivision(equation)
         if '/' in req:
             x,y = req.split('/')
             string = str(float(x) / float(y))
             equation = formatEquation(equation.replace(req,string))
             return multiplicationDivision(equation)
     else:
         return equation
 def removeBrackets(equation):
     '''
     计算算式中括号里的公式，直到所有括号的计算已完成
     '''
     re_rule =  r'\([^()]*\)'
     equation = formatEquation(equation)
     if re.search(re_rule,equation):
         req = re.search(re_rule,equation).group()
         string = addSubtract(multiplicationDivision(req[1:-1]))
         equation = equation.replace(req,string)
         return removeBrackets(equation)
     else:
         return equation
 if __name__ == '__main__':
     while 1:
         #equation = input("请输入需要计算的公式")
         equation = "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) )"
         equation = equation.replace(' ','')
         #判断字符是否合法
         if findErrorChar(equation) :
             errorChar = findErrorChar(equation)
             print("下列字符不合法：",''.join(errorChar))
         elif findErrorOperator(equation):
             errorOperator = findErrorOperator(equation)
             print("下列字符不合法：",''.join(errorOperator))
         else:
             #格式化算式
             formatEquation(equation)
             print("输入的公式为：",equation)
             #去除括号
             equation = removeBrackets(equation)
             #计算结果
             equation = addSubtract(multiplicationDivision(equation))
             print('程序计算结果为：',equation)
             print('eval计算结果为：',eval(equation))
             break

源代码