Author: Saravana Kumar

Method Overriding in Python | Easy Explanation with Examples
🔹 What is Method Overriding?

Method Overriding means:

A child class (subclass) writes its own version of a method that already exists in the parent class (superclass).
- It helps the child class change or improve the behavior of a parent method.
- The method name must be same in both classes.
🔸 Real-Life Example:

Imagine a general printer prints in black & white. But a color printer overrides that function and prints in color.

🔹 Basic Example of Method Overriding:
```
class Animal:
    def speak(self):
        print("Animal speaks")

class Dog(Animal):
    def speak(self):  # Overriding the parent's method
        print("Dog barks")

d = Dog()
d.speak()  # Output: Dog barks
```
✅ Dog class has its own version of the speak() method.

🔹 Why Use Method Overriding?

✅ To customize behavior
✅ To add extra work in child class
✅ To make code flexible and clean

🔹 Calling Parent Method Using super()

Sometimes we want to call the original (parent) method also:
```
class Animal:
    def speak(self):
        print("Animal speaks")

class Dog(Animal):
    def speak(self):
        super().speak()  # Call parent method
        print("Dog barks")

d = Dog()
d.speak()
```
🟢 Output:
```
Animal speaks
Dog barks
```
🔹 Another Example: Bank Account
```
class Account:
    def show_balance(self):
        print("Balance is $1000")

class SavingsAccount(Account):
    def show_balance(self):
        print("Savings balance is $1500")

a = SavingsAccount()
a.show_balance()
```
📝 Practice Questions with Answers

❓ Q1: Create a class Shape with a method draw(). Override it in Circle and Square.

✅ Answer:
```
class Shape:
    def draw(self):
        print("Drawing a shape")

class Circle(Shape):
    def draw(self):
        print("Drawing a circle")

class Square(Shape):
    def draw(self):
        print("Drawing a square")

c = Circle()
s = Square()

c.draw()
s.draw()
```
❓ Q2: Create a class Employee with method work(). Override it in Manager and Developer.

✅ Answer:
```
class Employee:
    def work(self):
        print("Employee works")

class Manager(Employee):
    def work(self):
        print("Manager manages the team")

class Developer(Employee):
    def work(self):
        print("Developer writes code")

m = Manager()
d = Developer()

m.work()
d.work()
```
🧾 Summary

Term Meaning
Overriding Child class redefines parent method
Method Name Must be the same in both classes
Use of super() To call the parent class method from child

🎯 Quick Recap
- Method Overriding = Changing a parent method in the child class.
- Useful when child class needs a different behavior.
- super() helps to use parent’s method with the new one.
July 6, 2025
Polymorphism in Python | One Name, Many Uses
🔹 What is Polymorphism?

The word Polymorphism means:

Poly = many, morph = form
So, Polymorphism = many forms

📌 In Python, the same function or method can work in different ways depending on the object.

🔹 Why Use Polymorphism?

✅ Makes code flexible
✅ Easy to understand and update
✅ Helps work with different objects in a similar way

🔹 Example: Polymorphism with Functions
```
def add(a, b):
    return a + b

print(add(3, 4))        # Numbers
print(add("Hi ", "Tom"))  # Strings
```
✅ Same function name add() works with numbers and strings — this is polymorphism.

🔹 Polymorphism with Classes

Let’s see two different classes using the same method name:
```
class Dog:
    def speak(self):
        print("Dog barks")

class Cat:
    def speak(self):
        print("Cat meows")

def animal_sound(animal):
    animal.speak()

d = Dog()
c = Cat()

animal_sound(d)
animal_sound(c)
```
✅ Different objects (Dog, Cat) use the same method speak() in different ways.

🔹 Polymorphism with Inheritance
```
class Vehicle:
    def move(self):
        print("Vehicle is moving")

class Car(Vehicle):
    def move(self):
        print("Car is driving")

class Boat(Vehicle):
    def move(self):
        print("Boat is sailing")

def start_trip(vehicle):
    vehicle.move()

v1 = Car()
v2 = Boat()

start_trip(v1)
start_trip(v2)
```
✅ move() method works differently for each object. This is runtime polymorphism.

🔹 Built-in Polymorphism Example
```
print(len("Python"))       # Output: 6
print(len([1, 2, 3, 4]))    # Output: 4
print(len((10, 20, 30)))    # Output: 3
```
✅ len() function works with string, list, tuple — same function name, many forms.

📝 Practice Questions with Answers

❓ Q1: Create a method called greet() in two classes: English and Spanish.

✅ Answer:
```
class English:
    def greet(self):
        print("Hello")

class Spanish:
    def greet(self):
        print("Hola")

def say_hello(obj):
    obj.greet()

e = English()
s = Spanish()
say_hello(e)
say_hello(s)
```
❓ Q2: Write a function that accepts any shape class and prints area using area() method.

✅ Answer:
```
class Circle:
    def area(self):
        print("Area of Circle: πr²")

class Square:
    def area(self):
        print("Area of Square: side²")

def print_area(shape):
    shape.area()

c = Circle()
s = Square()
print_area(c)
print_area(s)
```
🧾 Summary Table

Term Meaning
Polymorphism One method or function, many forms
Built-in Functions like len(), +, etc.
User-defined Methods in different classes with same name

🎯 Quick Recap
- Polymorphism helps the same method name work in different ways.
- It can be seen in:
  - Functions
  - Classes
  - Inheritance
  - Built-in functions
July 6, 2025

Term	Meaning
Overriding	Child class redefines parent method
Method Name	Must be the same in both classes
Use of `super()`	To call the parent class method from child

Term	Meaning
Polymorphism	One method or function, many forms
Built-in	Functions like `len()`, `+`, etc.
User-defined	Methods in different classes with same name

Inheritance in Python | Learn How One Class Can Use Another

🔹 What is Inheritance?

Inheritance means a class (child) can use the data and functions from another class (parent).
This helps us reuse code and build bigger programs easily.

📌 Real-life example: A child gets features from parents — like eyes, language, habits.
Same way, a class gets methods and data from another class.

🔹 Why Use Inheritance?

✅ Reuse old code
✅ Add new features easily
✅ Clean and simple design
✅ Avoid writing same code again

🔹 Basic Example: Simple Inheritance

class Animal:
    def speak(self):
        print("Animal speaks")

class Dog(Animal):  # Inherits Animal
    def bark(self):
        print("Dog barks")

d = Dog()
d.speak()  # From parent
d.bark()   # From child

🔸 Types of Inheritance in Python (with Examples)

Python supports 5 types of inheritance:

1. Single Inheritance

One parent class → One child class

class Parent:
    def show(self):
        print("This is Parent")

class Child(Parent):
    def display(self):
        print("This is Child")

c = Child()
c.show()
c.display()

2. Multilevel Inheritance

Parent → Child → Grandchild

class Grandfather:
    def house(self):
        print("Grandfather's house")

class Father(Grandfather):
    def car(self):
        print("Father's car")

class Son(Father):
    def bike(self):
        print("Son's bike")

s = Son()
s.house()
s.car()
s.bike()

3. Hierarchical Inheritance

One parent → Many children

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

class Dog(Animal):
    def bark(self):
        print("Dog barks")

class Cat(Animal):
    def meow(self):
        print("Cat meows")

d = Dog()
c = Cat()
d.sound(); d.bark()
c.sound(); c.meow()

4. Multiple Inheritance

Child class inherits from two or more parent classes

class Father:
    def job(self):
        print("Father is a teacher")

class Mother:
    def cook(self):
        print("Mother cooks food")

class Child(Father, Mother):
    def play(self):
        print("Child plays cricket")

c = Child()
c.job()
c.cook()
c.play()

5. Hybrid Inheritance

Combination of multiple types (e.g., multiple + multilevel)

class A:
    def a(self):
        print("Class A")

class B(A):
    def b(self):
        print("Class B")

class C:
    def c(self):
        print("Class C")

class D(B, C):  # Combines B (from A) + C
    def d(self):
        print("Class D")

obj = D()
obj.a()
obj.b()
obj.c()
obj.d()

🔹 Using `super()` to Access Parent Constructor

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

class Student(Person):
    def __init__(self, name, grade):
        super().__init__(name)  # call parent __init__
        self.grade = grade

s = Student("Arun", "A")
print(s.name, s.grade)

📝 Practice Questions with Answers

❓ Q1: Create a base class `Vehicle`, and `Car`, `Bike` should inherit from it.

✅ Answer:

class Vehicle:
    def start(self):
        print("Vehicle starts")

class Car(Vehicle):
    def drive(self):
        print("Car drives")

class Bike(Vehicle):
    def ride(self):
        print("Bike rides")

c = Car()
c.start(); c.drive()

b = Bike()
b.start(); b.ride()

❓ Q2: Show multilevel inheritance using `Company`, `Manager`, `Employee`.

✅ Answer:

class Company:
    def company_name(self):
        print("XYZ Ltd")

class Manager(Company):
    def manage(self):
        print("Manages team")

class Employee(Manager):
    def work(self):
        print("Works on project")

e = Employee()
e.company_name()
e.manage()
e.work()

🧾 Summary Table

Inheritance Type	Structure Example
Single	A → B
Multilevel	A → B → C
Hierarchical	A → B, A → C
Multiple	A + B → C
Hybrid	Combination of above

📣 Coming Up Next:

➡️ Polymorphism in Python | One Name, Many Forms (Easy Guide)

July 6, 2025

Encapsulation in Python | Easy OOP Explanation for Beginners

🔹 What is Encapsulation?

Encapsulation means hiding data and keeping it safe.
In Python, we use class to keep variables and functions together.
It helps to protect the data from being changed accidentally.

📌 Think of a capsule – it keeps medicine safely inside.
Encapsulation keeps data and code safely inside the class.

🔹 Why Encapsulation?

✅ Easy to use
✅ Protects data
✅ Only allow limited access
✅ Clean and secure code

🔹 Example: Without Encapsulation

class Student:
    def __init__(self, name, marks):
        self.name = name
        self.marks = marks

s1 = Student("Arun", 85)
print(s1.marks)  # Anyone can access and change

s1.marks = 40  # Can be changed easily
print(s1.marks)

🔐 Example: With Encapsulation (using private variable)

class Student:
    def __init__(self, name, marks):
        self.name = name
        self.__marks = marks  # private variable

    def get_marks(self):     # getter
        return self.__marks

    def set_marks(self, value):  # setter
        if value >= 0 and value <= 100:
            self.__marks = value
        else:
            print("Invalid marks!")

s1 = Student("Arun", 85)
print(s1.get_marks())  # Output: 85

s1.set_marks(95)       # Valid update
print(s1.get_marks())  # Output: 95

s1.set_marks(150)      # Invalid update

🔎 What is `__` (double underscore)?

It makes the variable private.
Cannot access it directly like s1.__marks
Must use getter and setter methods.

🧠 Real-Life Example:

ATM Machine:

You can see balance, add money, withdraw money – but you can’t open the system.
That is encapsulation.

📝 Practice Questions with Answers

❓ Q1: Create a class `BankAccount` with private balance. Add `deposit()` and `get_balance()` methods.

✅ Answer:

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

    def deposit(self, amount):
        if amount > 0:
            self.__balance += amount

    def get_balance(self):
        return self.__balance

acc = BankAccount(1000)
acc.deposit(500)
print("Balance:", acc.get_balance())  # Output: 1500

❓ Q2: Make a class `Person` with private `age`. Use `set_age()` to update age with condition (must be > 0).

✅ Answer:

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

    def get_age(self):
        return self.__age

    def set_age(self, new_age):
        if new_age > 0:
            self.__age = new_age
        else:
            print("Invalid age!")

p1 = Person("Ravi", 25)
print(p1.get_age())
p1.set_age(-10)  # Invalid
p1.set_age(30)   # Valid
print(p1.get_age())  # 30

📘 Summary

Word	Meaning
Encapsulation	Hide data inside class using private vars
`__`	Makes variable private
Getter	Function to get value
Setter	Function to set value safely

📣 Coming Up Next:

➡️ Inheritance in Python | Learn How One Class Can Use Another

July 6, 2025

What is self in Python? | Easy Explanation with Examples

🔹 What is `self` in Python?

self means this object.
It helps Python know which object we are talking about.
It is used inside class functions to access the object’s data and functions.

📌 Important Points:

self is not a keyword. You can name it anything (but using self is the rule).
It is sent automatically when you call a function using an object.

🔹 Example 1: Using `self` to store data

class Student:
    def __init__(self, name, age):
        self.name = name  # save name
        self.age = age    # save age

    def show(self):
        print("Name:", self.name)
        print("Age:", self.age)

s1 = Student("Arun", 18)
s1.show()

✅ Output:

Name: Arun
Age: 18

🔹 How `self` works:

Let’s understand:

self.name = name → store the value in the object.
self.age = age → same for age.
Later, inside the show() function, we again use self.name to get the data back.

🔹 Example 2: Use `self` in multiple objects

class Car:
    def __init__(self, brand):
        self.brand = brand

    def start(self):
        print(self.brand, "is starting...")

c1 = Car("Toyota")
c2 = Car("BMW")

c1.start()  # Toyota is starting...
c2.start()  # BMW is starting...

👉 Here, self.brand is different for each object.

🔹 Example 3: Change values using `self`

class Employee:
    def __init__(self, name, salary):
        self.name = name
        self.salary = salary

    def change_salary(self, new_salary):
        self.salary = new_salary

    def show(self):
        print("Name:", self.name)
        print("Salary:", self.salary)

e1 = Employee("Ravi", 30000)
e1.change_salary(40000)
e1.show()

✅ Output:

Name: Ravi
Salary: 40000

📝 Practice Questions with Answers

❓ Q1: Create a class `Laptop` with `brand` and `price`. Use `self` to store and print data.

✅ Answer:

class Laptop:
    def __init__(self, brand, price):
        self.brand = brand
        self.price = price

    def show(self):
        print("Brand:", self.brand)
        print("Price:", self.price)

l1 = Laptop("HP", 55000)
l1.show()

❓ Q2: Create a class `Circle` with radius. Use a method to calculate area. (Area = 3.14 × radius × radius)

✅ Answer:

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

    def area(self):
        return 3.14 * self.radius * self.radius

c = Circle(5)
print("Area:", c.area())

🧾 Summary Table

Term	Meaning
`self`	Refers to current object inside a class
Use	To access variables and methods in object

📣 Next:

➡️ “Encapsulation in Python | Easy OOP Explanation for Beginners”

July 6, 2025

Author: Saravana Kumar

Method Overriding in Python | Easy Explanation with Examples

🔹 What is Method Overriding?

🔸 Real-Life Example:

🔹 Basic Example of Method Overriding:

🔹 Why Use Method Overriding?

🔹 Calling Parent Method Using super()

🔹 Another Example: Bank Account

📝 Practice Questions with Answers

❓ Q1: Create a class Shape with a method draw(). Override it in Circle and Square.

❓ Q2: Create a class Employee with method work(). Override it in Manager and Developer.

🧾 Summary

🎯 Quick Recap

Polymorphism in Python | One Name, Many Uses

🔹 What is Polymorphism?

🔹 Why Use Polymorphism?

🔹 Example: Polymorphism with Functions

🔹 Polymorphism with Classes

🔹 Polymorphism with Inheritance

🔹 Built-in Polymorphism Example

📝 Practice Questions with Answers

❓ Q1: Create a method called greet() in two classes: English and Spanish.

❓ Q2: Write a function that accepts any shape class and prints area using area() method.

🧾 Summary Table

🎯 Quick Recap

Inheritance in Python | Learn How One Class Can Use Another

🔹 What is Inheritance?

🔹 Why Use Inheritance?

🔹 Basic Example: Simple Inheritance

🔸 Types of Inheritance in Python (with Examples)

1. Single Inheritance

2. Multilevel Inheritance

3. Hierarchical Inheritance

4. Multiple Inheritance

5. Hybrid Inheritance

🔹 Using super() to Access Parent Constructor

📝 Practice Questions with Answers

❓ Q1: Create a base class Vehicle, and Car, Bike should inherit from it.

❓ Q2: Show multilevel inheritance using Company, Manager, Employee.

🧾 Summary Table

📣 Coming Up Next:

Encapsulation in Python | Easy OOP Explanation for Beginners

🔹 What is Encapsulation?

🔹 Why Encapsulation?

🔹 Example: Without Encapsulation

🔐 Example: With Encapsulation (using private variable)

🔎 What is __ (double underscore)?

🧠 Real-Life Example:

📝 Practice Questions with Answers

❓ Q1: Create a class BankAccount with private balance. Add deposit() and get_balance() methods.

❓ Q2: Make a class Person with private age. Use set_age() to update age with condition (must be > 0).

📘 Summary

📣 Coming Up Next:

What is self in Python? | Easy Explanation with Examples

🔹 What is self in Python?

📌 Important Points:

🔹 Example 1: Using self to store data

🔹 How self works:

🔹 Example 2: Use self in multiple objects

🔹 Example 3: Change values using self

📝 Practice Questions with Answers

❓ Q1: Create a class Laptop with brand and price. Use self to store and print data.

❓ Q2: Create a class Circle with radius. Use a method to calculate area. (Area = 3.14 × radius × radius)

🧾 Summary Table

📣 Next:

🔹 Calling Parent Method Using `super()`

❓ Q1: Create a class `Shape` with a method `draw()`. Override it in `Circle` and `Square`.

❓ Q2: Create a class `Employee` with method `work()`. Override it in `Manager` and `Developer`.

❓ Q1: Create a method called `greet()` in two classes: `English` and `Spanish`.

❓ Q2: Write a function that accepts any shape class and prints area using `area()` method.

🔹 Using `super()` to Access Parent Constructor

❓ Q1: Create a base class `Vehicle`, and `Car`, `Bike` should inherit from it.

❓ Q2: Show multilevel inheritance using `Company`, `Manager`, `Employee`.

🔎 What is `__` (double underscore)?

❓ Q1: Create a class `BankAccount` with private balance. Add `deposit()` and `get_balance()` methods.

❓ Q2: Make a class `Person` with private `age`. Use `set_age()` to update age with condition (must be > 0).

🔹 What is `self` in Python?

🔹 Example 1: Using `self` to store data

🔹 How `self` works:

🔹 Example 2: Use `self` in multiple objects

🔹 Example 3: Change values using `self`

❓ Q1: Create a class `Laptop` with `brand` and `price`. Use `self` to store and print data.

❓ Q2: Create a class `Circle` with radius. Use a method to calculate area. (Area = 3.14 × radius × radius)