Initialization

Instances are commonly created with specific parameters that distinguish them from one another. For instance, let's consider the class User and its instances, such as John and Bob, who have distinct names, surnames, and ages. Now, let's explore how we can set these parameters when creating an instance.

What is init ?

__init__ is a special method that is used to initialize attributes for a new instance of a class. The __init__ method, which is executed we create a new instance of a class.

As a reminder, creating a new instance involves using the class name and parentheses (). The purpose of the __init__ method is to receive values as arguments within these parentheses and assign these values to the attributes of the newly created instance.


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class User:
    def __init__(self, name, surname, age):
        self.name = name
        self.surname = surname
        self.age = age
        
bob = User("Bob", "Smith", 11)

print(bob.name, bob.surname, bob.age)

In the provided example, we have defined the __init__ method, which is executed every time a new instance of the class is created. When we create the bob instance, we pass the values "Bob", "Smith", and 11 as arguments to the User class. The __init__ method receives these arguments and utilizes them to define new attributes for the bob instance.

The User.age should raise an AttributeError because the User class does not have any attributes defined. The __init__ method, as mentioned earlier, is responsible for defining attributes for each instance of the class, not for the class itself.

Note

Further details about methods will be described in subsequent chapters.

We will cover the self argument in the next chapter. There is no need to delve into it at this moment.

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In-Depth Python OOP

Initialization

What is __init__ ?

What is init ?