Lesson 19: Python Classes, Objects, and OOP | Coding Class Series

---

Lesson 19: Python Classes, Objects, and OOP | Coding Class Series

Introduction

Welcome to Lesson 19!
In this lesson, we will learn about Object-Oriented Programming (OOP) in Python, including classes, objects, attributes, and methods.
OOP helps in writing organized, reusable, and modular code.

---

1. What is a Class?

A class is a blueprint for creating objects.
It defines attributes (data) and methods (functions) that the objects will have.

Example:

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

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

---

2. Creating Objects

my_dog = Dog("Buddy", "Golden Retriever")
print(my_dog.name)  # Output: Buddy
print(my_dog.breed) # Output: Golden Retriever
my_dog.bark()       # Output: Buddy says Woof!

---

3. Instance vs Class Attributes

• Instance attributes – unique for each object
• Class attributes – shared by all objects

Example:

class Dog:
    species = "Canis familiaris"  # class attribute

    def __init__(self, name, breed):
        self.name = name           # instance attribute
        self.breed = breed

dog1 = Dog("Buddy", "Golden Retriever")
dog2 = Dog("Max", "Beagle")

print(dog1.species)  # Canis familiaris
print(dog2.species)  # Canis familiaris

---

4. Methods

Methods are functions inside classes:

• Instance methods – operate on instance data
• Class methods – operate on class data
• Static methods – utility methods that don’t access class or instance data

Example:

class Circle:
    pi = 3.14159

    def __init__(self, radius):
        self.radius = radius

    def area(self):
        return Circle.pi * self.radius ** 2

c = Circle(5)
print(c.area())  # Output: 78.53975

---

5. Inheritance

Inheritance allows a class to use attributes and methods of another class.

Example:

class Animal:
    def eat(self):
        print("Eating")

class Dog(Animal):
    def bark(self):
        print("Woof!")

dog = Dog()
dog.eat()  # Eating
dog.bark() # Woof!

---

6. Practice Exercises

1. Create a class Car with attributes make, model, and year, and a method to display info.
2. Create two objects of Car and print their details.
3. Add a class method to count the number of cars created.
4. Implement inheritance with a Truck class derived from Car with an extra method load_cargo.

---