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MohammadReza Mahdian
MohammadReza Mahdian

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BasicOOP-Ch.1

#programming #beginners #tutorial #oop

Object-Oriented Thinking

MohammadRezaMahdian – November 2025
November 15, 2025

What is OOP?

Imagine you're building with LEGO. Every brick is an object — it has a shape, a color, and it does something.
OOP is just that: organizing your code like a LEGO set.

Why bother?

Your program starts small. Then it grows. And suddenly? Chaos.
OOP keeps things clean, fixable, and easy to grow. Fewer headaches down the road.

The 4 Core Ideas

  • Class — the blueprint
  • Polymorphism — same command, different behavior
  • Inheritance — borrow from a parent
  • Composition — build from smaller pieces

Class = Blueprint

A class says: “Here’s what something is, and what it can do.”

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

    def bark(self):           # action
        print("Woof!")
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Object = Real Thing

Now make a real dog:

my_dog = Dog("Rex", "German Shepherd")
my_dog.bark()
# → Woof!
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Has-A = Composition

Ask: “What does this thing have?” → That’s composition.

A Car has an Engine. Take the engine out? No car.

class Engine:
    def start(self):
        print("Engine running")

class Car:
    def __init__(self):
        self.engine = Engine()  # Car HAS an Engine

    def drive(self):
        self.engine.start()
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Strong bond — parts live and die with the whole.

Is-A = Inheritance

Ask: “What is this thing?” → That’s inheritance.

A PoliceCar is a Car.

class PoliceCar(Car):
    def siren(self):
        print("Wee-woo!")
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Now it can drive() and siren().

Hide the Mess (Encapsulation)

Don’t let anyone poke the insides.

class BankAccount:
    def __init__(self):
        self.__balance = 500  # hidden

    def deposit(self, amount):
        self.__balance += amount

    def get_balance(self):
        return self.__balance
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Only through deposit() and get_balance().

Getters & Setters 

def get_speed(self):
    return self.speed

def set_speed(self, value):
    if value >= 0:
        self.speed = value
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Class vs Object

Class Object
Blueprint Real instance
One definition Many copies
In code In memory

Composition vs Aggregation

  • Composition: Strong → Engine dies with Car
  • Aggregation: Weak → Players can leave Team 
class Player:
    pass

class Team:
    def __init__(self):
        self.players = []

    def add_player(self, p):
        self.players.append(p)
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How to Design

  1. What does it have? → attributes
  2. What does it do? → methods

Cat → name, age → meow(), sleep()

Objects Talk 

car.drive()
account.deposit(100)
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Keep It Clean

Hide complexity. Reuse. Build step by step.

Bottom Line

OOP isn’t magic. It’s thinking about code like real life.
Makes big programs manageable.

MohammadRezaMahdian – Nov 2025

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