Python多分支实现四则运算器

class calculator:#定义计算器类，包含加减乘除和小数位
    def __init__(self,a,b):
        self.a =a
        self.b = b
    def addition(self,retain):
        return round(self.a+self.b, retain)
    def division(self,retain):
        return round(self.a/self.b, retain)
    def subtraction(self,retain):
        return round(self.a-self.b, retain)
    def multiplication(self, retain):
        return round(self.a*self.b, retain)
while 1:#一直循环计算下去
    getNum1 = input('请输入第一个数:')
    try:
        float(getNum1)#判断是否为数字
    except ValueError:
        print("Error")#不是数字则输出Error，程序终止
        break
    opera = input('请输入符号:')#输入加减乘除运算符号
    getNum2 = input("请输入第二个数:")
    try:
        float(getNum2)
    except ValueError:
        print("Error")
        break
    getRetain = input('请输入保留小数位数:')
    result = 0.00
    num1 = float(getNum1)
    num2 = float(getNum2)
    Retain = int(getRetain)#计算小数位
    if opera =='+':
        result = calculator(num1,num2).addition(Retain)
    elif opera =='-':
        result = calculator(num1,num2).subtraction(Retain)
    elif opera =='*':
        result = calculator(num1,num2).multiplication(Retain)
    else:
        result = calculator(num1,num2).division(Retain)
    print(result)