--- title: Classes & Objects slug: classes-objects category: oop order: 1 difficulty: intermediate estimatedMinutes: 18 prerequisites: - defining - dictionaries tags: - classes - objects - oop --- # Classes & Objects Object-Oriented Programming (OOP) lets you model real-world things as **objects** with attributes and behaviors. ## Defining a Class class Dog: def __init__(self, name, breed): self.name = name self.breed = breed def bark(self): return f"{self.name} says Woof!" my_dog = Dog("Rex", "Labrador") print(my_dog.name) print(my_dog.bark()) ## The __init__ Method `__init__` is the **constructor** — it runs when you create a new object: class Rectangle: def __init__(self, width, height): self.width = width self.height = height def area(self): return self.width * self.height def perimeter(self): return 2 * (self.width + self.height) rect = Rectangle(5, 3) print(f"Area: {rect.area()}") print(f"Perimeter: {rect.perimeter()}") ## The self Parameter `self` refers to the current instance. It gives each object its own data: class Counter: def __init__(self): self.count = 0 def increment(self): self.count += 1 def get_count(self): return self.count c1 = Counter() c2 = Counter() c1.increment() c1.increment() c2.increment() print(f"c1: {c1.get_count()}") # 2 print(f"c2: {c2.get_count()}") # 1 ## Challenges Create a `Person` class with `name` and `age`, and a `greet()` method that prints the greeting. class Person: def __init__(self, name, age): pass def greet(self): pass p = Person("Alice", 25) p.greet() Store `name` and `age` as `self.name` and `self.age` in `__init__`, then use them in `greet()`. class Person: def __init__(self, name, age): self.name = name self.age = age def greet(self): print(f"Hello, my name is {self.name} and I am {self.age} years old") p = Person("Alice", 25) p.greet() Create a `Rectangle` class with `width` and `height`, and an `area()` method. Print the area of a 5x3 rectangle. class Rectangle: pass rect = Rectangle(5, 3) print(f"Area: {rect.area()}") Define `__init__` to accept width/height and an `area` method that returns `self.width * self.height`. class Rectangle: def __init__(self, width, height): self.width = width self.height = height def area(self): return self.width * self.height rect = Rectangle(5, 3) print(f"Area: {rect.area()}")