Now we have the base Aircraft class we can refactor by hoisting into it other common functionality. For example, both the initializer and registration() methods are identical between the two subtypes:

class Aircraft:

    def __init__(self, registration):
        self._registration = registration

    def registration(self):
        return self._registration

    def num_seats(self):
        rows, row_seats = self.seating_plan()
        return len(rows) * len(row_seats)


class AirbusA319(Aircraft):

    def model(self):
        return "Airbus A319"

    def seating_plan(self):
        return range(1, 23), "ABCDEF"


class Boeing777(Aircraft):

    def model(self):
        return "Boeing 777"

    def seating_plan(self):
        # For simplicities sake, we ignore complex
        # seating arrangement for first-class
        return range(1, 56), "ABCDEGHJK"

These derived classes only contain the specifics for that aircraft type. All general functionality is shared from the base class by inheritance.

Thanks to duck-typing, inheritance is less used on Python than in other languages. This is generally seen as a good thing because inheritance is a very tight coupling between classes.