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.

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