A1.8 Inheritance, polymorphism and overriding worksheet

Subclasses and super, overriding, polymorphism, and abstract, virtual and static methods, with robot behaviours as subclasses.

Questions 5 marks in all

[1 mark]What does this program print?

class Robot:
    def __init__(self, name):
        self.name = name
    def greet(self):
        return "I am " + self.name

class Rover(Robot):
    def greet(self):
        return super().greet() + " and I rove"

class Drone(Robot):
    pass

for r in [Rover("R1"), Drone("D1")]:
    print(r.greet())

[1 mark]What is polymorphism?

AThe same method call behaving differently depending on the class of the object it is called on
BA class inheriting from two superclasses
CHiding an object's attributes
DCreating many objects from one class

[1 mark]What is true of an abstract class?

AIt cannot be instantiated, and its abstract methods must be overridden by subclasses
BIt has no attributes
CIt cannot have subclasses
DAll its methods are static

[1 mark]A static method is called as Motor.clamp(120). What can it not do?

AUse the attributes of a particular object
BTake parameters
CReturn a value
DBe called from another method

[1 mark]Inheritance models which relationship between a subclass and its superclass? Answer with two words.

The task: behaviours by inheritance

The starter has the superclass Behaviour, with a name attribute and an act() method. Write three subclasses from the class diagram. Each constructor calls super().__init__ with the behaviour's name, and each overrides act() so that it does its job and then prints <name> done: - Chirp(note): name chirp; stores note (a frequency in Hz) and its act plays that note twice, 0.2 seconds each time. - Square(size): name square; stores size (cm) and its act drives a square with sides of size cm, turning right 90 degrees at each corner. - Spin(): name spin; its act turns right a full 360 degrees. Then make the list routine = [Chirp(523), Square(20), Spin(), Chirp(784)] and call act() on each object in order with one loop. Do not use isinstance or type: polymorphism chooses the method.

# the two lines every program starts with: the commands, then the robot
from bugbot import *
connect()

class Behaviour:
    def __init__(self, name):
        self.name = name

    def act(self):
        print(self.name, "does nothing")

routine = [Behaviour("chirp"), Behaviour("square")]
for behaviour in routine:
    behaviour.act()

Plan your program here, then type it in and press Run.

Do it on the robot
www.bugbotlab.com/learn/a1-8-inheritance-and-polymorphism/
The simulator checks it and tells you when it passes. Nothing to install, no account.

Challenges

Add a Pause(seconds) subclass that does not override act. What does it print, and why?

Make Behaviour abstract with Python's abc module and @abstractmethod. What happens now when you try Behaviour("test")?

Add a Polygon(sides, size) subclass, then make Square a subclass of Polygon. How much of Square is left?

What this lesson is about

Questions 5 marks in all

The task: behaviours by inheritance

Challenges