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Solve the following problem using Python, implementing the functions described below, one line at a time
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Description:
 def airplane(self, model_mask: str = '###') -> str: """Generate a dummy airplane model. :param model_mask: Mask of truck model. Here '@' is a placeholder of characters and '#' is a placeholder of digits. :return: Airplane model. :Example: Boeing 727. """

        model = self.random.custom_code(mask=model_mask)
        plane = self.random.choice(AIRPLANES)
        return '{} {}'.format(plane, model)