Python __str__

Summary: in this tutorial, you’ll learn how to use the Python __str__ method to make a string representation of a class.

Introduction to the Python __str__ method

Let’s start with the Person class:

class Person: def __init__(self, first_name, last_name, age): self.first_name = first_name self.last_name = last_name self.age = age
Code language: Python (python)

The Person class has three instance attributes including first_name, last_name, and age.

The following creates a new instance of the Person class and display it:

person = Person('John', 'Doe', 25) print(person)
Code language: Python (python)

Output:

<__main__.Person object at 0x0000023CA16D13A0>
Code language: Python (python)

When you use the print() function to display the instance of the Person class, the print() function shows the memory address of that instance.

Sometimes, it’s useful to have a string representation of an instance of a class. To customize the string representation of a class instance, the class needs to implement the __str__ magic method.

Internally, Python will call the __str__ method automatically when an instance calls the str() method.

Note that the print() function converts all non-keyword arguments to strings by passing them to the str() before displaying the string values.

The following illustrates how to implement the __str__ method in the Person class:

class Person: def __init__(self, first_name, last_name, age): self.first_name = first_name self.last_name = last_name self.age = age def __str__(self): return f'Person({self.first_name},{self.last_name},{self.age})'
Code language: Python (python)

And when you use the print() function to print out an instance of the Person class, Python calls the __str__ method defined in the Person class. For example:

person = Person('John', 'Doe', 25) print(person)
Code language: Python (python)

Output:

Person(John,Doe,25)
Code language: Python (python)

Summary

  • Implement the __str__ method to customize the string representation of an instance of a class.
Did you find this tutorial helpful ?