Class Representation Special Methods: Python OOP Complete Course — Part 15

Learn what are class representation special methods in Python OOP and how to override them.

Before we start let me tell you that:

• This article is a part of The Complete Course in Object-Oriented Programming in Python which you can find it here.
• All resources are available in the “Resources” section below.
• This article is also available as a YouTube video here.

Introduction

Assume that you have a Student class with an object from this class student1 . When you print this object, you will get the following ugly result.

class Student:
     pass

student1 = Student()
print (student1)

Output:

<__main__.Student object at 0x0000017FCB084088>

The question now is: how to override this behavior in order to get a better representation? For example (students' IDs or students' names)?

To learn how to do that, keep reading :)

Table of Contents

1. What are Class Representation Special Methods?
2. Available Class Representation Special Methods
3. How to Override Class Representation Special Methods?

1. What are Class Representation Special Methods?

They are the methods that are used to generate a representative value for your class objects.

The representative value could be:

• A human-readable string of your object state, the values of instance attributes. For example, if you want to know some information about the object just by printing that object.
• A machine-readable string to help regenerate the object itself.
• A hash value for the object to give each object a unique ID.

2. Available Class Representation Special Methods

There are a lot of methods under this category. In this article, the two main special methods will be covered. These methods are:

• __str__(): This method defines the behavior for when the function str() is called with an object of your class.
• __repr__(): This method defines the behavior for when the function repr() is called with an object of your class.

To keep the article clean and concise, all of these methods’ definitions have been moved to this pdf file.

3. How to Override Class Representation Special Methods?

• First, let us start talking about__str__() method

Assume that you have Student class which has the following instance attributes (id, first_name, last_name, full_name, age, and classess), and a student object. Let us print the result of str() method.

Output:

<__main__.Student object at 0x0000000004DCD6A0>

You got an ugly output that tells you the type of the object and in which memory location it is stored.

Now, let us override the __str__() method in order to get a human-readable string. Refer to the last method in the following code…

Output:

I am John Doe and my age is 25

Nice, right !!

• Now let us talk about __repr__() method

Let us use the previous Student class and the previous student object. Try to print the result of repr() method.

Output:

<__main__.Student object at 0x0000000004DD7C88>

As you have seen, you got an ugly output again.

Now, let us override the __repr__() method in order to generate a machine-readable string. Refer to the last method in the following code…

Output:

Student("John", "Doe", 25)

In the previous example, you got a machine-readable string that you can use directly to redefine exactly the same Student object as follows:

student = Student("John", "Doe", 25)
print(repr(student))

Output:

Student("John", "Doe", 25)

Now, let us summarize what we have learned in this article.

• Class Representation Special Methods are the methods that are used to generate a representative value for your class objects.
• __str__(): is used usually to generate a human-readable string.
• __repr__(): is used usually to generate a machine-readable string.

P.S.: A million thanks for your time reading my story. Before you leave let me mention quickly two points:

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To get back to the previous article, you can use the following link:

Part 14:Operators Special Methods

To move on to the next article, you can use the following link:

Part 16:How to Make Your Class Objects Convertible to Other Data Types

Resources:

• GitHub here.
• Class Representation Special Methods pdf file