Day 18: Python programming

*Abstraction & Interface *

1. What is Abstraction?

Abstraction means showing only essential details and hiding implementation.

Real life example:

• Driving a car → you only use steering, brake, accelerator


• Engine working → hidden

2. Why Abstraction is Needed?

✔ Reduces complexity

✔ Improves security

✔ Improves maintainability

✔ Forces standard structure

✔ Used in real projects

3. Abstract Class

An abstract class:

• Cannot create object


• Can contain abstract & normal methods


• Must be inherited
  In Python we use abc module.

4. Abstract Base Class (ABC)

from abc import ABC, abstractmethod

Abstract Method

A method without body; must be implemented by child class.

5. Example – Abstract Class

from abc import ABC, abstractmethod

class Shape(ABC):

@abstractmethod

def area(self):

pass

Cannot create object:

s = Shape() # Error

6. Implement Abstract Method in Child Class

class Square(Shape):

def init(self, side):

self.side = side

def area(self):

return self.side * self.side

sq = Square(5)

print(sq.area())

7. Multiple Abstract Methods

class Vehicle(ABC):

@abstractmethod

def start(self):

pass

@abstractmethod

def stop(self):

pass

8. Interface in Python

Python does not have interface keyword like Java.

Abstract class with only abstract methods behaves like an interface.

9. Interface Example

class Bank(ABC):

@abstractmethod

def deposit(self, amt):

pass

@abstractmethod

def withdraw(self, amt):

pass

10. Implementing Interface

class SBI(Bank):

def deposit(self, amt):

print("Deposit:", amt)

def withdraw(self, amt):

    print("Withdraw:", amt)

b = SBI()

b.deposit(5000)

b.withdraw(2000)

11. Abstract Class with Normal Methods

class Employee(ABC):

def office_rules(self):

print("Office time 9AM - 6PM")

@abstractmethod

def salary(self):

pass

12. Child Class Implementation

class Developer(Employee):

def salary(self):

print("Salary: 40,000")

d = Developer()

d.office_rules()

d.salary()

13. Important Rules of Abstraction

✔ Cannot create object of abstract class

✔ All abstract methods must be implemented

✔ Use ABC + abstractmethod

✔ Abstract class may have normal methods

✔ Used for code standards

14. Real-Time Example – Payment System

class Payment(ABC):

@abstractmethod

def pay(self, amount):

pass

class GooglePay(Payment):

def pay(self, amount):

print("Paid", amount, "using GooglePay")

class PhonePe(Payment):

def pay(self, amount):

print("Paid", amount, "using PhonePe")

15. Why Interface/Abstraction in Projects?

✔ Multiple developers work together

✔ Fixed method structure

✔ Easy to update or extend

✔ Safer code

✔ Cleaner architecture