Lesson 3: Inheritance & Polymorphism

⏱ ~40 min Lesson 3 of 14 💚 Free

What You'll Learn

Create child classes that inherit from a parent class
Override methods and call the parent using super()
Understand polymorphism — one interface, many behaviors
Use isinstance() and issubclass()

Inheritance

Inheritance lets a new class (child/subclass) automatically get all the attributes and methods of an existing class (parent/superclass). You extend it by adding new methods or overriding existing ones.

Inheritance models "is-a" relationships: a Dog is-an Animal. A SavingsAccount is-a BankAccount.

super()

When a child class overrides __init__, it should usually call super().__init__(...) to run the parent's setup code first. super() returns a proxy to the parent class and works correctly even in complex multiple-inheritance hierarchies.

super().__init__(name, age) — runs the parent constructor so parent attributes are set before adding child-specific ones.

Polymorphism

Polymorphism means "many forms." In Python, different classes can define the same method name, and calling that method on any of them produces the correct behavior for that object's type. This lets you write code that works with any compatible object without checking its type manually.

Duck typing: "If it walks like a duck and quacks like a duck, it's a duck." Python cares whether an object has the right method — not what class it is.

Quick Check

1. What does super().__init__() do in a child class?

Creates a new parent object

Calls the parent class's __init__ to run parent setup code

Deletes the parent class

Prevents the child from overriding any more methods

2. Which relationship does inheritance model?

has-a (e.g., Car has-a Engine)

is-a (e.g., Dog is-a Animal)

uses-a (e.g., Controller uses-a Database)

contains-a (e.g., List contains-a Item)

3. Polymorphism allows you to call animal.speak() on a Dog, Cat, or Bird without knowing which type. What makes this work?

All animals are stored in the same list type

Each subclass defines its own speak() method and Python dispatches the correct one

Python converts all objects to the parent type before calling the method

You must use isinstance() before every method call

4. What does isinstance(dog, Animal) return if Dog inherits from Animal?

False — dog is a Dog, not an Animal

True — a subclass instance is also an instance of the parent class

An error is raised

None