init

Learn the constructor with __init__.

The init method

__init__ is a special method called automatically when an instance is created. It is used to set up instance attributes; hence it is called the constructor.

Example: class User:\n def __init__(self, name):\n self.name = name. When you write u = User("Alex"), __init__ runs and u.name becomes "Alex". The name starts and ends with two underscores; this marks special methods.

Assigning attributes with self

Inside __init__ you assign the parameter to an instance attribute with self.name = name. self points to the instance being created.

Example: def __init__(self, name, age):\n self.name = name\n self.age = age. Then u = User("Alex", 30) makes both u.name and u.age ready. The parameter and attribute names do not have to match, but it is a common choice.

Exercise Add init to the User class

Define a class named User. Add the method def __init__(self, name): and in the body write self.name = name. After the class, create an instance with u = User("Alex") and print u.name.

Show example solution

# Define the User class and the __init__ method
class User:
    def __init__(self, name):
        self.name = name

u = User("Alex")
print(u.name)

Test yourself

When does __init__ run?
- When the class is defined
- Automatically when the script starts
- When a method is called
- When an instance is created with User("Alex")
Show answer

When an instance is created with User("Alex") — __init__ is called automatically when an instance is created.

Complete the __init__ signature

class User:
    def __init__(self, ____):
        self.name = name

Show answer

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

Match the __init__ concepts

__init__

Constructor
self.name

Instance attribute
User("Alex")

Instantiation

Next lesson: __str__ and __repr__

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