Object-Oriented Programming in Python (OOP) - Tutorial

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Contents:

1. Introduction to Classes & Objects
   • What is a class? (Blueprint for objects)
   • What is an object? (Instance of a class)
2. How to Create a Class
   • Basic syntax: class MyClass:
   • Naming conventions (PascalCase).
3. The __init__ Method (Constructor)
   • Purpose: Initialize object attributes.
   • Syntax: def __init__(self, ...)
4. The self Keyword (Explain early—it’s everywhere!)
   • What is self? (Reference to the instance).
   • Why it’s needed (access attributes/methods).
5. Instantiating Objects
   • How to create an object: obj = MyClass().
   • How __init__ is called automatically.
6. Adding Attributes to a Class
   • Instance attributes (per-object, e.g., self.name = name).
   • Class attributes (shared, e.g., class_var = 0).
   • Class vs. Instance Variables (Compare them here).
7. Defining Methods in a Class
   • What are methods? (Functions inside a class).
   • Example: def greet(self): print("Hello!").
8. Passing Arguments to Methods
   • Methods with parameters: def set_age(self, age):.
   • Default arguments (e.g., def __init__(self, name="Anonymous")).
9. Practical OOP Examples (Apply all concepts!)
   • Example 1: A Dog class with name, breed, bark().
   • Example 2: A Car class with make, model, year, and describe().
   • Example 3: A Student class with name, age, grade simple
   • Example 4: A BankAccount class with balance, deposit(), and withdraw().
   • Example 5: A Student class with name, age, grade, and methods like introduce().

their name, age, and grade.

1. Introduction to Classes & Objects

Class

• A class is a blueprint for creating objects.
• Defines the structure (attributes & methods) that objects will have.
• Example: A Car class defines properties like color, model, and actions like drive().

Object

• An object is an instance of a class.
• Created from the class blueprint.
• Example: A Toyota car (object) created from the Car class.

2. How to Create a Class

Syntax

class ClassName:  
    # Attributes & methods go here  

• Naming Convention: Use PascalCase (e.g., MyClass, BankAccount).

3. The __init__ Method (Constructor)

Purpose

• Automatically called when an object is created.
• Used to initialize attributes (set initial values).

Syntax

def __init__(self, param1, param2):  
    self.attribute1 = param1  
    self.attribute2 = param2  

• Example:

  class Dog:  
    def __init__(self, name):  
        self.name = name  # Initialize 'name' attribute  
  

4. The self Keyword

What is self?

• Refers to the current instance of the class.
• Used to access attributes & methods inside the class.

Why is it needed?

• Without self, Python wouldn’t know which object’s attributes to modify.
• Example:

  class Dog:  
    def __init__(self, name):  
        self.name = name  # 'self.name' belongs to this Dog object  
  

5. Instantiating Objects

How to Create an Object

object_name = ClassName(arguments)  

• Example:

  my_dog = Dog("Buddy")  # Calls __init__ automatically  
  

6. Adding Attributes to a Class

Instance Attributes

• Unique to each instance (object) of a class.
• Store data specific to that object.
• Defined within the __init__ constructor method, using the self parameter.

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

Class Attributes

• Shared by all objects of the class.
• Defined outside __init__.

  class Dog:  
    species = "Canine"  # Class attribute (shared)  
  

Class vs. Instance Attributes

| Feature | Class Attribute | Instance Attribute |
|————–|—————-|——————-|
| Scope | Shared by all objects | Unique per object |
| Defined | Outside __init__ | Inside __init__ |

7. Defining Methods in a Class

What are Methods?

• Functions defined inside a class.
• Must take self as the first parameter.

Example

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

my_dog = Dog()  
my_dog.bark()  # Output: "Woof!"  

8. Passing Arguments to Methods

Methods with Parameters

class Dog:  
    def set_age(self, age):  
        self.age = age  

my_dog = Dog()  
my_dog.set_age(3)  # Sets age to 3  

Default Arguments

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

dog1 = Dog()          # name = "Unknown"  
dog2 = Dog("Buddy")   # name = "Buddy"  

9. Practical OOP Examples

Example 1: Dog Class

class Dog:  
    species = "Canine"  # Class attribute  

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

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

# Create objects  
dog1 = Dog("Buddy", "Labrador")  
dog2 = Dog("Max", "Beagle")  

dog1.bark()  # Output: "Buddy says Woof!"  

Example 2: Car Class

class Car:
    def __init__(self, make, model, year):
        self.make = make
        self.model = model
        self.year = year

    def describe(self):
        print(f"{self.year} {self.make} {self.model}")

my_car = Car("Toyota", "Corolla", 2020)
my_car.describe()  # Output: 2020 Toyota Corolla

Example 3: Student Class

# Class Definition
class Student:
    # Constructor
    def __init__(self, name, age, grade): # self refers to the current object being created.
        self.name = name
        self.age = age
        self.grade = grade
    # Method
    def info(self):
        print(f"Name = {self.name} Age = {self.age} Grade = {self.grade}")

# Object Creation

student1 = Student("Hamza", 8, 3)
student2 = Student("Muhammad", 15, 10)

# Accessing Attributes and Methods

print(student1.name)
student1.info()
student2.info()

Example 4: BankAccount Class

class BankAccount:  
    def __init__(self, balance=0):  
        self.balance = balance  

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

    def withdraw(self, amount):  
        if amount <= self.balance:  
            self.balance -= amount  
        else:  
            print("Insufficient funds!")  

# Usage  
account = BankAccount(100)  
account.deposit(50)  
account.withdraw(30)  
print(account.balance)  # Output: 120  

Example 5: Student Class

Represents a student with their name, age, and grade.

class Student:

    def __init__(self, name, age, grade):
        """Initializes a Student object with the given attributes."""
        self.name = name
        self.age = age
        self.grade = grade

    def get_name(self):
        """Returns the student's name."""
        return self.name

    def get_age(self):
        """Returns the student's age."""
        return self.age

    def get_grade(self):
        """Returns the student's grade."""
        return self.grade

    def set_grade(self, new_grade):
        """Updates the student's grade."""
        self.grade = new_grade

    def introduce(self):
        """Prints a self-introduction message."""
        print("Hello, my name is", self.name, "and I'm in grade", self.grade)

# Example usage
student1 = Student("Hamza", 8, 3)
student2 = Student("Muhammad", 16, 10)

student1.introduce()  # Output: Hello, my name is Alice and I'm in grade 9
print(student2.get_name())  # Output: Bob
student2.set_grade(11)
print(student2.get_grade())  # Output: 11

Python Tutorial in Urdu: How to Create a Class

Python Tutorial: Python Classes - What is Class Constructor

Python Tutorial in Urdu: How to Create Classes and Instance Attributes

References and Bibliography

• Classes - Python documentation
• Python Attributes – Class and Instance Attribute Examples - freecodecamp.org

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