Classes & Objects

Creating a class

A class is a blueprint for creating objects. Use the class keyword.

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

    def bark(self):
        print(f"{self.name} says woof!")

my_dog = Dog("Rex")
my_dog.bark()

__init__ and self

__init__ is the constructor — it runs when you create a new object. self refers to the current instance.

class Car:
    def __init__(self, brand, speed):
        self.brand = brand
        self.speed = speed

    def describe(self):
        print(f"{self.brand} goes {self.speed} km/h")

c = Car("Toyota", 180)
c.describe()

Try it yourself

Run the example below. Edit it and see what changes.

class Cat:
    def __init__(self, name):
        self.name = name
    def meow(self):
        print(f"{self.name} says meow!")

c = Cat("Whiskers")
c.meow()
 

Common mistakes

• ⚠Forgetting self as the first parameter of methods.
• ⚠Not calling __init__ correctly — it's called automatically.
• ⚠Confusing class attributes (shared) with instance attributes (per-object).