Python Academy · Lesson

Classes and the init Method

Define classes, create objects, and initialize attributes.

Lesson 1 of 413 steps

Classes and the __init__ Method is a free Python Academy lesson on CoddyKit. This is lesson 1 of 4. You can read the complete lesson below for free — then practise it hands-on in the browser with a built-in code editor and a 24/7 AI tutor. It is part of the Python Academy learning path, and your progress syncs across the web and the CoddyKit app. The Python Academy course includes 4 lessons in total.

Defining a Class

Use the class keyword to define a class. By convention, class names use CapWords.

class Dog:
    pass

fido = Dog()
print(type(fido))  # <class '__main__.Dog'>

The init Method

__init__ is called automatically when an object is created. Use it to set up instance attributes.

class Dog:
    def __init__(self, name, breed):
        self.name = name
        self.breed = breed

fido = Dog("Fido", "Labrador")
print(fido.name)   # Fido

self Explained

self refers to the current instance. It must be the first parameter of every instance method. Python passes it automatically.

class Counter:
    def __init__(self):
        self.count = 0

    def increment(self):
        self.count += 1

c = Counter()
c.increment()
print(c.count)  # 1

Multiple Instances

Each instance has its own copy of instance attributes set in __init__.

class Point:
    def __init__(self, x, y):
        self.x = x
        self.y = y

p1 = Point(1, 2)
p2 = Point(5, 7)
print(p1.x, p2.x)  # 1 5

Default Parameter Values in init

Give __init__ parameters default values to make some arguments optional.

class Circle:
    def __init__(self, radius=1.0):
        self.radius = radius

c1 = Circle()
c2 = Circle(5)
print(c1.radius, c2.radius)  # 1.0 5

Instance Methods

Methods defined inside a class operate on the instance via self.

class Rectangle:
    def __init__(self, w, h):
        self.w = w
        self.h = h

    def area(self):
        return self.w * self.h

r = Rectangle(4, 5)
print(r.area())  # 20

Adding Attributes After Creation

You can add attributes to an instance after creation, but it is cleaner to declare all of them in __init__.

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

p = Person("Alice")
p.age = 30      # added after creation
print(p.name, p.age)

The init Return Value

__init__ must return None. Returning anything else raises a TypeError.

class Broken:
    def __init__(self):
        return 42   # TypeError!

# Correct
class OK:
    def __init__(self):
        self.value = 42
        # implicit return None

Checking Instance Type

Use isinstance() to check if an object is an instance of a class.

class Animal:
    pass

class Dog(Animal):
    pass

d = Dog()
print(isinstance(d, Dog))     # True
print(isinstance(d, Animal))  # True

dict Attribute

Every instance stores its attributes in a __dict__ dictionary.

class Book:
    def __init__(self, title, pages):
        self.title = title
        self.pages = pages

b = Book("Python 101", 300)
print(b.__dict__)  # {'title': 'Python 101', 'pages': 300}

Deleting Attributes

Use del to remove an attribute from an instance at runtime.

class Config:
    def __init__(self):
        self.debug = True
        self.version = "1.0"

cfg = Config()
del cfg.debug
print(hasattr(cfg, "debug"))  # False

Quick Check

What is the purpose of self in Python class methods?

Answer it in the interactive lesson

Recap

Classes are blueprints for objects. __init__ initializes instance attributes, self refers to the current object, and each instance maintains its own attribute dictionary.

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Frequently Asked Questions

Is the “Classes and the init Method” lesson free?

Yes — the full text of “Classes and the __init__ Method” is free to read here on the web. To practise it interactively (a built-in code editor and a 24/7 AI tutor) and unlock the rest of the Python Academy course, upgrade to CoddyKit PRO. The Python Academy course includes 4 lessons in total.

What will I learn in “Classes and the init Method”?

Define classes, create objects, and initialize attributes. You practise Python Academy with hands-on code you run directly in the browser, and a 24/7 AI tutor answers your questions as you work through the lesson.

Do I need any experience to start Python Academy?

No prior experience is required. Python Academy on CoddyKit is structured for beginners through advanced learners, so you can start here or from the beginning and move at your own pace. This is lesson 1 of 4.

How long does the “Classes and the init Method” lesson take?

Most CoddyKit lessons take about 5–10 minutes. Each one is bite-sized and interactive, so you make steady progress and pick up exactly where you left off across the web and the app.

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