Classes & Objects

A class is a blueprint

A class describes a kind of thing: what data it has and what it can do. Objects are the actual things made from it.

class Dog:
    def __init__(self, name, age):
        self.name = name    # data (attributes)
        self.age = age

    def bark(self):         # behavior (methods)
        return f"{self.name} says woof!"

rex = Dog("Rex", 3)
luna = Dog("Luna", 5)
print(rex.bark())
print(luna.name, luna.age)

• __init__ runs when you create an object. It sets up the data.
• self is "this particular object", so Rex and Luna each keep their own name.

Watch objects get built

Why classes matter for your career

Most large codebases (and many interview questions) are organized around classes: User, Order, ShoppingCart, PaymentProcessor. The idea of keeping data and the code that changes it together is called encapsulation. It's the first pillar of object-oriented programming, which you'll go deeper into in the OOP & Clean Code course.

Special methods

Methods with double underscores let your objects work with Python's built-in features:

class Money:
    def __init__(self, cents):
        self.cents = cents

    def __str__(self):
        return f"${self.cents / 100:.2f}"

    def __add__(self, other):
        return Money(self.cents + other.cents)

print(Money(250) + Money(199))