简单工厂模式

class Operation():

    def __init__(self, NumberA=0, NumberB=0):
        self.NumberA = NumberA
        self.NumberB = NumberB

    def GetResult(self):
        pass


class AddOp(Operation):

    def GetResult(self):
        return self.NumberB + self.NumberA


class MinusOp(Operation):

    def GetResult(self):
        return self.NumberA - self.NumberB


class MultiOp(Operation):

    def GetResult(self):
        return self.NumberA * self.NumberB


class DivideOp(Operation):

    def GetResult(self):
        try:
            return 1.0 * self.NumberA / self.NumberB
        except ZeroDivisionError:
            raise


class OperationFatory():

    def ChooseOperation(self, op):
        if op == '+':
            return AddOp()
        if op == '-':
            return MinusOp()
        if op == '*':
            return MultiOp()
        if op == '/':
            return DivideOp()


if __name__ == '__main__':
    ch = ''
    while not ch == 'q':
        NumberA = float(input('Please input number1:  '))
        op = input('Please input the operation:  ')
        NumberB = float(input('Please input number2:  '))
        OPFactory = OperationFatory()
        OPType = OPFactory.ChooseOperation(op)
        OPType.NumberA = NumberA
        OPType.NumberB = NumberB
        print('The result is:', OPType.GetResult())
        print('
#--  input q to exit any key to continue')
        try:
            ch = input()
        except:
            ch = ''