[Leejohnston]

Chapter 18 — Object-Oriented Programming (Beginner Overview)
OOP (Object-Oriented Programming) lets you organise code around “objects” — things that have properties and behaviour.

At first it can feel strange, but once you understand it, everything clicks.

Games, apps, websites, simulations, AI systems — almost all major programs use OOP.

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18.1 What Is an Object?

An object is a bundle of:

• data (attributes) 
• behaviour (methods/functions) 

Example in real life: 
A **Dog** has:

• attributes → name, age, colour 
• behaviours → bark(), eat(), sleep()

Programming copies this idea.

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18.2 Creating a Class

A class is a blueprint for making objects.

Code:

class Dog:
    pass

This creates a “Dog type”, but it has no data yet.

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18.3 The __init__ Method

This runs when you create (instantiate) an object.

Code:

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

self refers to the specific object created.

Create a dog:

Code:

my_dog = Dog("Rex", 4)

Access attributes:

Code:

print(my_dog.name)
print(my_dog.age)

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18.4 Adding Methods (Object Behaviours)

Code:

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

    def bark(self):
        print(self.name + " says: Woof!")

Use it:

Code:

d = Dog("Buddy")
d.bark()

Output:

Code:

Buddy says: Woof!

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18.5 Multiple Objects From One Class

Code:

d1 = Dog("Max")
d2 = Dog("Bella")

d1.bark()
d2.bark()

Each object is separate.

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18.6 Updating Attributes

Code:

d = Dog("Luna")
d.age = 3

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18.7 Example — Simple Character Class

Code:

class Character:
    def __init__(self, name, health):
        self.name = name
        self.health = health

    def take_damage(self, amount):
        self.health -= amount
        print(f"{self.name} now has {self.health} HP")

Use it:

Code:

hero = Character("Astra", 100)
hero.take_damage(15)

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18.8 Why OOP Is Useful

OOP makes your programs:

• more organised 
• easier to expand 
• cleaner to maintain 
• great for large projects 
• realistic (objects model real things)

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18.9 Inheritance (Beginner Peek)

A class can reuse and extend another class.

Code:

class Animal:
    def sound(self):
        print("Some sound")

class Cat(Animal):
    def sound(self):
        print("Meow")

Cat automatically has everything Animal has — but can also override behaviour.

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18.10 Mini Project — Bank Account Class

Your class must include:

• __init__(owner, balance) 
• deposit(amount) 
• withdraw(amount) 
• show_balance() 

Example:

Code:

Account: Lee
Balance: £120

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18.11 Challenge — RPG Fighter Class

Create a class with:

• name 
• health 
• attack_power 

Functions:

• attack(other_character) 
• heal(amount) 
• status()

Example battle:

Code:

Astra attacks Vorn for 12 damage!
Vorn now has 58 HP.

BONUS: 
Add critical hits (random 1.5× damage).

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18.12 Chapter Summary

• a class is a blueprint 
• objects are created from that blueprint 
• attributes = data 
• methods = behaviour 
• __init__ runs automatically 
• self refers to the current object 
• OOP creates bigger, cleaner, scalable programs 

Next:
Chapter 19 — Practical Project: Building a Mini Python Game

This chapter turns everything learned so far into a small but exciting playable project.

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Written and Compiled by Lee Johnston — Founder of The Lumin Archive