Methods Inside Classes – CSUK:Coder

Introduction

So far, you’ve learned how to:

Create classes
Use __init__ to store data
Use self to give each object its own attributes

In this lesson, you’ll learn how to:

Define methods inside a class
Use self to access object data inside methods
Call methods on objects

Methods allow objects to do things, not just store data.

What Is a Method?

A method is a function that belongs to a class.

It is:

Defined inside a class
Automatically given access to the object using self

Example: A Method Inside a Class

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

    def say_hello(self):
        print('Hello, my name is', self.name)

student = Student('Alex')
student.say_hello()

What’s happening here?

say_hello is a method
self.name accesses data stored in the object
The method is called using dot notation

Predict:

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

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

    def introduce(self):
        print('My name is', self.name)

student1 = Student('Alex')
student2 = Student('Jamie')

student1.introduce() 
student2.introduce()

Think about:

Will both students print the same message?
How does the method know which name to use?

Run:

Run the code below and check your prediction.

Investigate:

Now let’s explore what happens when a method uses more than one attribute.

Try this:

Add an attribute called year_group
Update the method so it prints both the name and year group

Use the editor below to experiment.

Think about:

Why does the method not need parameters for name?
How does self help the method access the correct data?

Modify:

The following code contains a mistake — the method cannot access the object’s data correctly.

Fix the code so the method works as intended.

The problem

The method is missing self
Python doesn’t know which object is being used

Hint:

Methods must always include self as the first parameter.