Lesson 47: Classes and Objects

Introduction to Classes and Objects

Object-Oriented Programming (OOP) is a programming paradigm that organizes code into objects. A class is a blueprint for creating objects, and an object is an instance of a class. OOP helps organize code, make it reusable, and model real-world concepts.

Classes allow you to bundle data (attributes) and functions (methods) together, making your code more organized and easier to maintain.

Defining a Class

Use the class keyword to define a class. The __init__ method is a special method called when an object is created:

defining_class.py
# Define a class
class Dog:
    def __init__(self, name, age):
        self.name = name
        self.age = age
    
    def bark(self):
        print(f"{self.name} says Woof!")
    
    def get_info(self):
        return f"{self.name} is {self.age} years old"

# Create objects (instances)
dog1 = Dog("Buddy", 3)
dog2 = Dog("Max", 5)

# Use the objects
dog1.bark()  # Buddy says Woof!
print(dog2.get_info())  # Max is 5 years old

Attributes and Methods

Attributes store data, and methods are functions that belong to the class:

attributes_methods.py
class Person:
    def __init__(self, name, age):
        # Attributes
        self.name = name
        self.age = age
    
    # Method
    def introduce(self):
        print(f"Hi, I'm {self.name} and I'm {self.age} years old.")
    
    def have_birthday(self):
        self.age += 1
        print(f"Happy birthday! {self.name} is now {self.age}.")

person = Person("Alice", 25)
person.introduce()  # Hi, I'm Alice and I'm 25 years old.
person.have_birthday()  # Happy birthday! Alice is now 26.
print(person.age)  # 26

The self Parameter

The self parameter refers to the instance of the class. It's automatically passed when you call a method on an object:

self_parameter.py
class Car:
    def __init__(self, brand, model):
        self.brand = brand  # self refers to this instance
        self.model = model
    
    def start(self):
        print(f"{self.brand} {self.model} is starting...")

# When you call car.start(), Python automatically passes the car object as self
car = Car("Toyota", "Camry")
car.start()  # self is automatically car

Best Practices

✅ Class Design Tips

• Use descriptive class names (PascalCase)

• Keep classes focused on a single responsibility

• Use __init__ to initialize attributes

• Always include self as the first parameter in methods

• Use methods to modify object state, not direct attribute access