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class Calculator:    def __init__(self, a, b):        self.a = a        self.b = b    def addition(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)    def division(self, retain):        return round(self.a / self.b, retain)while True:    try:        num1 = float(input('???????:'))        num2 = float(input('???????:'))        operator = input('??????:')        retain = int(input('?????????:'))    except ValueError:        print("Error")        break    if operator not in ['+', '-', '*', '/']:        print("Error")        break    result = Calculator(num1, num2).{        '+' if operator == '+' else        '-' if operator == '-' else        '*' if operator == '*' else        '/' if operator == '/' else    }(retain)    print(result)

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