Introduction

In object-oriented programming, we often find that different classes share common features.

Instead of rewriting the same code again and again, we can use a powerful idea called inheritance.

Inheritance allows:

  • One class to reuse the attributes and methods of another
  • Code to be organised more logically
  • Programs to be easier to extend and maintain

In this lesson, you will learn how:

  • A child class can inherit from a parent class
  • Shared behaviour can be written once
  • Specialised behaviour can be added in child classes

Parent and Child Classes

A parent class (also called a base class) contains general attributes and methods.

A child class (also called a subclass) inherits everything from the parent, and can:

  • Use the parent’s methods
  • Add new methods
  • Override existing methods

Basic Inheritance Syntax 

class Parent:
    def method(self):
        print("This is from the parent")

class Child(Parent):
    pass

The key part is:

  • class Child(Parent):

This tells Python that Child inherits from Parent.

Example: Person and Student 

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

    def introduce(self):
        print("Hello, my name is", self.name)

class Student(Person):
    pass

Even though Student has no code inside it, it still:

  • Has a name attribute
  • Can use the introduce() method

Predict:

Look at the code below. What do you think will be printed?

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

    def introduce(self):
        print("Hello, my name is", self.name)

class Student(Person):
    pass

student = Student("Alex")
student.introduce()

Think about:

  • Where is introduce() defined?
  • Does the Student class define it?
  • Why does the method still work?

Run:

Run the program below to check your prediction.

Investigate:

Child classes can also add their own methods.

Try this:

  • Add a method called study() to the Student class
  • Make it print "Studying..."
  • Call the method on the student object

Think about:

  • Which methods come from the parent?
  • Which methods belong only to the child?

Modify:

The following program is meant to demonstrate inheritance, but it contains an error.

Fix the code so that the student can introduce themselves correctly.

The problem

  • self is missing when accessing name
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