One of the things we'd like to do with our flight is accept seat bookings. To do that we need to know the seating layout, and for that we need to know the type of aircraft. Let's make a second class to model different kinds of aircraft:

class Aircraft:

    def __init__(self, registration, model, num_rows,   
                 num_seats_per_row):
        self._registration = registration
        self._model = model
        self._num_rows = num_rows
        self._num_seats_per_row = num_seats_per_row

    def registration(self):
        return self._registration

    def model(self):
        return self._model

The initializer creates four attributes for the aircraft: registration number, a model name, the number of rows of seats, and the number of seats per row. In a production code scenario we could validate these arguments to ensure, for example, that the number of rows is not negative.

This is straightforward enough, but for the seating plan we'd like something a little...