1 class Operation(): 2  3     def __init__(self, NumberA=0, NumberB=0): 4         self.NumberA = NumberA 5         self.NumberB = NumberB 6  7     def GetResult(self): 8         pass 9 10 11 class AddOp(Operation):12 13     def GetResult(self):14         return self.NumberB + self.NumberA15 16 17 class MinusOp(Operation):18 19     def GetResult(self):20         return self.NumberA - self.NumberB21 22 23 class MultiOp(Operation):24 25     def GetResult(self):26         return self.NumberA * self.NumberB27 28 29 class DivideOp(Operation):30 31     def GetResult(self):32         try:33             return 1.0 * self.NumberA / self.NumberB34         except ZeroDivisionError:35             raise36 37 38 class OperationFatory():39 40     def ChooseOperation(self, op):41         if op == '+':42             return AddOp()43         if op == '-':44             return MinusOp()45         if op == '*':46             return MultiOp()47         if op == '/':48             return DivideOp()49 50 51 if __name__ == '__main__':52     ch = ''53     while not ch == 'q':54         NumberA = float(input('Please input number1:  '))55         op = input('Please input the operation:  ')56         NumberB = float(input('Please input number2:  '))57         OPFactory = OperationFatory()58         OPType = OPFactory.ChooseOperation(op)59         OPType.NumberA = NumberA60         OPType.NumberB = NumberB61         print('The result is:', OPType.GetResult())62         print('\n#--  input q to exit any key to continue')63         try:64             ch = input()65         except:66             ch = ''