DEV Community: Karthick (k)

Projects focused on Python Object-Oriented Programming (OOP) concepts.

Karthick (k) — Wed, 14 Oct 2026 05:53:19 +0000

Library Management System

A simple console-based Library Management System built with Python.

Description

This project allows a librarian or users to manage books and members of a library.

It supports adding books, registering users, borrowing/returning books, searching books, and viewing user details.

Features

View all books with ID, title, author, and available quantity
Add new books
Search books by title (case-insensitive)
Borrow a book (only if available)
Return a book
View borrowed books of a specific user
Register new users
View all registered users
Pre-loaded with 10 sample books and 3 sample users

Classes Used

Class	Purpose
`Book`	Stores book details and manages quantity
`User`	Stores user details and borrowed books list
`Library`	Manages the collection of books and users

How to Run

Make sure you have Python 3 installed.
Save the code in a file named library_management.py
Open the terminal/command prompt
Run the command:

python library_management.py

class Book:
    def __init__(self, book_id, title, author, quantity):
        self.book_id = book_id
        self.title = title
        self.author = author
        self.quantity = quantity

    def display_book_info(self):
        print(f"ID: {self.book_id}, Title: {self.title}, Author: {self.author}, Available Quantity: {self.quantity}")

    def check_availability(self):
        return self.quantity > 0

    def update_quantity(self, change):
        self.quantity += change


class User:
    def __init__(self, user_id, name, place):
        self.user_id = user_id
        self.name = name
        self.place = place
        self.borrowed_books = []


    def borrow_book(self, book):
        if book.check_availability():
            self.borrowed_books.append(book)
            book.update_quantity(-1)
            print(f"{self.name} has borrowed '{book.title}'")
        else:
            print(f"Sorry, '{book.title}' is not available for borrowing.")

    def return_book(self, book):
        if book in self. borrowed_books:
            self.borrowed_books.remove(book)
            book.update_quantity(1)
            print(f"{self.name} has returned '{book.title}'")
        else:
            print(f"{self.name} does not have '{book.title}' borrowed.")

    def view_borrowed_books(self):
        if self.borrowed_books:
            print(f"{self.name}'s Borrowed Books:")
            for book in self. borrowed_books:
                print(f" - {book.title}")
        else:
            print(f"{self.name} has not borrowed any books.")

class Library:
    def __init__(self):
        self.books = []
        self.users = []

    def add_book(self, book):
        self.booksappend(book)

    def list_users(self):
        if self.users:
            print("\nRegistered Users:")
            for user in self.users:
                print(f"ID: {user.user_id}, Name: {user.name}, Place: {user.place}")
        else:
            print("No users registered yet.")

    def register_user(self, user):
        if any(u.user_id == user.user_id for u in self.users):
            print("User with the same ID already exists! Try another ID.")
            return
        self.usersappend(user)
        print(f"New user {user.name} added successfully.")

    def search_book_by_title(self, title):
        return [book for book in selfbooks if title.lower() in book.title.lower()]

    def list_books(self):
        if self.books:
            print("Books in the library:")
            for book in self. books:
                book.display_book_info()
        else:
            print("No books available in the library.")

    def add_new_book(self):
        book_id = int(input("Enter Book ID: "))
        if any(book.book_id == book_id for book in self.books):
            print("Book with the same ID already exists, please try another ID.")
            return

        title = input("Enter the book title: ")
        author = input("Enter author name: ")
        quantity = int(input("Enter the quantity of book: "))

        new_book = Book(book_id, title, author, quantity)
        self.add_book(new_book)
        print("Book added successfully!")
        new_book.display_book_info()


def main():
    library = Library()

    # Sample books
    book1 = Book(1, "Harry Potter and the Philosopher's Stone", "J.K. Rowling", 5)
    book2 = Book(2, "The Hobbit", "J.R.R. Tolkien", 3)
    book3 = Book(3, "1984", "George Orwell", 2)
    book4 = Book(4,"AI Rising: India’s Artificial Intelligence Growth Story"," Jayanth N. Kolla, Leslie D’Monte",5)
    book5 = Book(5, "The Great Gatsby", "F. Scott Fitzgerald", 4)
    book6 = Book(6, "To Kill a Mockingbird", "Harper Lee", 3)
    book7 = Book(7,"The Power of Critical Thinking","Richard Paul",5)
    book8 = Book(8, "From Dump to Design", "John Doe", 2)
    book9 = Book(9, "The Catcher in the Rye", "J.D. Salinger", 3)
    book10= Book(10, "The Alchemist", "Paulo Coelho", 4)

    library.add_book(book1)
    library.add_book(book2)
    library.add_book(book3)
    library.add_book(book4)
    library.add_book(book5)
    library.add_book(book6)
    library.add_book(book7)
    library.add_book(book8)
    library.add_book(book9)
    library.add_book(book10)

    # Sample users (now properly registered)
    user1 = User(1, "Karthick", "Chennai")
    user2 = User(2, "Kaviya", "Perambalur")
    user3 = User(3, "Praveen", "Trichy")

    library.register_user(user1)
    library.register_user(user2)
    library.register_user(user3)

    while True:
        print("\nWelcome to the Library Management System")
        print("1. View all books")
        print("2. Add Books")
        print("3. Search for a book by title")
        print("4. Borrow a book")
        print("5. Return a book")
        print("6. View borrowed books")
        print("7. Add new User")
        print("8. Exit")
        print("9. View all users")


        choice = input("Enter your choice: ")

        if choice == "1":
            library.list_books()

        elif choice == "2":
            library.add_new_book()

        elif choice == "3":
            title = input("Enter the book title to search: ")
            found_books = library.search_book_by_title(title)
            if found_books:
                for book in found_books:
                    book.display_book_info()
            else:
                print(f"No book found with the title '{title}'")

        elif choice == "4":
            user_id = int(input("Enter User ID: "))
            book_id = int(input("Enter Book ID to Borrow: "))
            user = next((u for u in library.users if u.user_id == user_id), None)
            book = next((b for b in library.books if b.book_id == book_id), None)
            if user and book:
                user.borrow_book(book)
            else:
                print("Invalid User ID or Book ID")

        elif choice == "5":
            user_id = int(input("Enter your user ID: "))
            book_id = int(input("Enter the book ID to return: "))
            user = next((u for u in library.users if u.user_id == user_id), None)
            book = next((b for b in library.books if b.book_id == book_id), None)
            if user and book:
                user.return_book(book)
            else:
                print("Invalid user or book ID.")

        elif choice == "6":
            user_id = int(input("Enter your user ID: "))
            user = next((u for u in library.users if u.user_id == user_id), None)
            if user:
                user.view_borrowed_books()
            else:
                print("Invalid user ID.")

        elif choice == "7":
            user_id = int(input("Enter user id: "))
            name = input("Enter user's name: ")
            place = input("Enter user's place: ")
            user = User(user_id, name, place)
            library.register_user(user)

        elif choice == "8":
            print("Exiting the system. Goodbye!")
            break
        elif choice == "9":
            library.list_users()

        else:
            print("Invalid choice, please try again.")


if __name__ == "__main__":
    main()

Inheritance in Python

Karthick (k) — Fri, 09 Oct 2026 03:36:29 +0000

Inheritance is a fundamental concept in object-oriented programming (OOP) that allows a class (called a child or derived class) to inherit attributes and methods from another class (called a parent or base class).

Here, a parent class Animal is created that has a method info(). Then a child class Dog is created that inherits from Animal and adds additional behaviour.

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

    def info(self):
        print("Animal name:", self.name)

class Dog(Animal):
    def sound(self):
        print(self.name, "barks")

d = Dog("Buddy")
# Inherited method
d.info()     
d.sound()

Output

Animal name: Buddy Buddy barks
Benefits Of Inheritance

Promotes code reusability by sharing attributes and methods across classes.
Models real-world hierarchies like Animal -> Dog or Person -> Employee.
Simplifies maintenance through centralised updates in parent classes.
Enables method overriding for customised subclass behaviour.
Supports scalable, extensible design using polymorphism.

How I Mastered React useState in One Day

Karthick (k) — Sun, 04 Oct 2026 05:27:42 +0000

Today, I decided to understand the most important hook in React: useState deeply. If you are preparing for an interview or just starting out, useState is the foundation of everything you will build.

Here is how I learned it, broken down into 4 simple examples.

What is useState?

useState is a built-in React Hook that gives functional components their own "memory". Without it, variables disappear when a component re-renders. It returns an array with two things: the current state and a function to update it.

const [state, setState] = useState(initialValue);

import React, { useState } from 'react';

export default function UseStatePlayground() {
  // 1. Number State (Counter)
  const [count, setCount] = useState(0);

  // 2. String State (Input Tracker)
  const [name, setName] = useState("");

  // 3. Boolean State (Toggle)
  const [isVisible, setIsVisible] = useState(false);

  // 4. Array State (Shopping List)
  const [items, setItems] = useState([]);
  const [inputValue, setInputValue] = useState("");

  const addItem = () => {
    if (inputValue.trim() !== "") {
      setItems([...items, inputValue]); // Spread operator to add to array
      setInputValue(""); // Clear input after adding
    }
  };

  return (
    <div style={{ padding: '20px', fontFamily: 'sans-serif' }}>
      <h2>React useState Practice</h2>

      {/* --- 1. Counter (Number) --- */}
      <div style={{ marginBottom: '20px' }}>
        <h3>1. Counter</h3>
        <p>Count: {count}</p>
        <button onClick={() => setCount(count + 1)}>Add 1</button>
      </div>

      {/* --- 2. Input Tracker (String) --- */}
      <div style={{ marginBottom: '20px' }}>
        <h3>2. Input Tracker</h3>
        <input 
          type="text" 
          value={name} 
          onChange={(e) => setName(e.target.value)} 
          placeholder="Type your name"
        />
        <p>Hello, {name || "stranger"}!</p>
      </div>

      {/* --- 3. Toggle (Boolean) --- */}
      <div style={{ marginBottom: '20px' }}>
        <h3>3. Toggle</h3>
        <button onClick={() => setIsVisible(!isVisible)}>
          {isVisible ? "Hide" : "Show"} Secret
        </button>
        {isVisible && <p>👑 The secret password is: ReactIsAwesome</p>}
      </div>

      {/* --- 4. Array (Shopping List) --- */}
      <div>
        <h3>4. Array List</h3>
        <input 
          type="text" 
          value={inputValue} 
          onChange={(e) => setInputValue(e.target.value)} 
          placeholder="Add an item"
        />
        <button onClick={addItem}>Add</button>
        <ul>
          {items.map((item, index) => (
            <li key={index}>{item}</li>
          ))}
        </ul>
      </div>
    </div>
  );
}

Discover the Power of Python’s Built-in Functions!

Karthick (k) — Tue, 29 Sep 2026 05:14:51 +0000

List of All the Functions
The table below lists all Python built-in functions along with a short description of each:

List of All the Functions in Python

In Python, built-in functions offer a variety of functionalities that make programming more efficient and streamlined. Below is a comprehensive table listing all Python built-in functions along with a brief description of each:

Function	Description
`abs()`	Returns the absolute value of a number.
`aiter()`	Returns an asynchronous iterator from an asynchronous iterable.
`all()`	Returns True if all elements in an iterable are true.
`anext()`	Returns the next item from an asynchronous iterator.
`any()`	Returns True if any element in an iterable is true.
`ascii()`	Returns a printable representation of an object.
`bin()`	Converts an integer to a binary string.
`bool()`	Converts a value to True or False.
`breakpoint()`	Starts the debugger at the current point in the program.
`bytearray()`	Returns a mutable byte array.
`bytes()`	Returns an immutable bytes object.
`callable()`	Checks whether an object can be called like a function.
`chr()`	Returns the character for a given Unicode code point.
`classmethod()`	Converts a method into a class method.
`compile()`	Compiles source code into a code object.
`complex()`	Creates a complex number.
`delattr()`	Deletes an attribute from an object.
`dict()`	Creates a dictionary.
`dir()`	Returns a list of an object's attributes and methods.
`divmod()`	Returns the quotient and remainder of two numbers.
`enumerate()`	Adds a counter to an iterable.
`eval()`	Evaluates a Python expression.
`exec()`	Executes dynamically created Python code.
`filter()`	Filters elements of an iterable using a function.
`float()`	Converts a value to a floating-point number.
`format()`	Formats a value according to a specified format.
`frozenset()`	Creates an immutable set.
`getattr()`	Returns the value of a specified attribute.
`globals()`	Returns the current global namespace as a dictionary.
`hasattr()`	Checks whether an object has a specified attribute.
`hash()`	Returns the hash value of an object.
`help()`	Displays the documentation for an object.
`hex()`	Converts an integer to a hexadecimal string.
`id()`	Returns the unique identity of an object.
`input()`	Reads input from the user as a string.
`int()`	Converts a value to an integer.
`isinstance()`	Checks whether an object is an instance of a class.
`issubclass()`	Checks whether a class is derived from another class.
`iter()`	Returns an iterator from an iterable.
`len()`	Returns the number of items in an object.
`list()`	Creates a list.
`locals()`	Returns the current local namespace as a dictionary.
`map()`	Applies a function to every item in an iterable.
`max()`	Returns the largest item.
`memoryview()`	Returns a memory view object.
`min()`	Returns the smallest item.
`next()`	Returns the next item from an iterator.
`object()`	Creates a new base object.
`oct()`	Converts an integer to an octal string.
`open()`	Opens a file and returns a file object.
`ord()`	Returns the Unicode code point of a character.
`pow()`	Returns the value of a number raised to a power.
`print()`	Prints values to the console.
`property()`	Creates a managed property for a class.
`range()`	Generates a sequence of numbers.
`repr()`	Returns the official string representation of an object.
`reversed()`	Returns a reverse iterator.
`round()`	Rounds a number to the specified number of digits.
`set()`	Creates a set of unique elements.
`setattr()`	Sets the value of an object's attribute.
`slice()`	Creates a slice object.
`sorted()`	Returns a new sorted list from an iterable.
`staticmethod()`	Converts a method into a static method.
`str()`	Converts a value to a string.
`sum()`	Returns the sum of all items in an iterable.
`super()`	Returns a proxy object to access methods of a parent class.
`tuple()`	Creates a tuple.
`type()`	Returns the type of an object or creates a new type.
`vars()`	Returns the `__dict__` attribute of an object.
`zip()`	Combines multiple iterables element-wise.
`__import__()`	Imports a module programmatically.

Thank you

Strings in Python

Karthick (k) — Sat, 26 Sep 2026 06:34:43 +0000

What Are Strings in Python?

A string is a sequence of characters enclosed in quotes. Characters can be letters, digits, symbols, spaces, or even special characters like newlines. In Python, strings are one of the most commonly used data types because almost every program deals with text in some form: names, messages, file paths, user input, and more.

Python treats strings as sequences, which means each character has a position (index), and you can access individual characters, extract substrings, and iterate over them just like you would with a list of items.

python
#1. String Indexing

name="python"

#3. String Immutability

# Strings in Python are immutable; once a string is created, you can't change any character in it. 
# If you try to assign a character anew to a specific index, Python raises a TypeError.abs
#4. String Methods

# Python provides a rich set of built-in methods for string manipulation. 
# These methods do not modify the original string cause strings are immutable; they return a new string.

python
#5. f-Strings (Formatted String Literals)
# Introduced in Python 3.6, f-strings are the most readable way to embed expressions inside the string
# Prefix the string with af andplace expressions inside curly braces {}.

name="Rohan"
age=16;

print(f'{name} is {age} year old')


#String Creation and Indexing
single="hello"
double="hello"

triple='''this is a multi-line string'''

print(single==double)
print(triple)

name="Ananya"

print(name[0])
print(name[-1])
print(name[3])
print(name[-2])

#String Immutability
name = "Vikram"

# Attempting to change a character causes an error
try:
    name[0] = "v"
except TypeError as e:
    print("Error:", e)


name = "u" + name[:-1]
print("New string:", name)


# Another approach using replace()
original = "LockeshKanagaraj"
modified = original.replace("LockeshKanagaraj", "KockeshKanagaraj")
print("Replace result:", modified)
print("Original unchanged:", original)

#Essential String Methods

text = "  Hello, World!  "


print(text.strip())

print()
print(text.lstrip())
print(text.rstrip())


name = "aarav sharma"

print(name.upper())
print(name.title())
print(name.capitalize())

sentence = "Python is fun and Python is powerful"

print(sentence.count(
    'powerful'
))

print(sentence.find("and"))
print(sentence.find("karhtic"))

print()

print(sentence.replace("and","king is"))

# split() - break string into a list
sentence = "Maths Science English Hindi"
words = sentence.split()
print(words)


csv_data = "Aarav,Priya,Rohan,Meera"

name=csv_data.split()
print(name)

result="-".join(name)
print(result)


print()

letters = ['P', 'y', 't', 'h', 'o', 'n']
word=''.join(letters)
print(word)

## split with maxsplit

data="one:two:three:four"
print(data.split(":",2))

#f-Strings and .format()

name="priyaa"

marks=92.567;


print(f'Student:{name}')
print(f'Marks : {marks:.2f}')
print(f"Double marks: {marks * 2}")
print(f"Name in uppercase: {name.capitalize()}")

print()
# .format() method
print("Hello, {}! You scored {}%.".format("Rohan", 85.000))
print("Pi is {:.4f}".format(3.14159))
print("{0} and {1} and {0}".format("Coding", "Maths"))


# Padding and alignment with f-strings
for i in range(1, 4):
    print(f"{i:>5} | {i*i:<5} | {i*i*i:^5}")

#Checking Methods and ord()/chr()


print("12345".isdigit())

print("12.4".isdigit())

print("Hehl2lo".isalpha()) 

print("abc123".isalnum()) 

print("Python3".startswith("Py"))
print("script.py".endswith(".py"))



print()

# ord() and chr()
print(ord('A'))   # 65
print(ord('a'))   # 97
print(chr(65))    # A
print(chr(97))    # a
print(ord('0'))   # 48
print(chr(199))

print()
# Character arithmetic
letter = 'C'
next_letter = chr(ord(letter) + 1)
print(f"Next letter after {letter} is {next_letter}")

#String Multiplication and Concatenation


line="="*40

print(line)

pattern="AB"*6 
print(pattern)

# Concatenation
first = "Modern"
last = "Coders"
full = first + " Age " + last
print(full)


name = "Aarav"
age = 14
# This causes an error: name + " is " + age
# Fix with str():
result = name + " is " + str(age)
print(result)
print(f"{name} is {age}")

List Comprehension in Python

Karthick (k) — Thu, 24 Sep 2026 12:51:07 +0000

List comprehension is a concise way to create new lists by applying an expression to each item in an existing iterable like a list, tuple or range. It helps to write clean, readable and efficient code compared to traditional loops.

Suppose you want to square every number in a list:

a = [2, 3, 4, 5]
res = [val ** 2 for val in a]
print(res)

Output

[4, 9, 16, 25]

Explanation: res = [val ** 2 for val in a] use **list comprehension **to create a new list by squaring each number in a.

Syntax

[expression for item in iterable if condition]

Parameters:

expression: operation or value to include in the new list.
item: current element from the iterable.
iterable: sequence like a list, tuple or range.
if condition (optional): filter to include only items that satisfy the condition.

Conditional Statements in List Comprehension

List comprehensions can use conditions to select or transform items based on specific rules. This allows creating customised lists more concisely and improves code readability and efficiency.

Example 1: This code uses a list comprehension with a condition to create a new list with only even numbers from list a.

a = [1, 2, 3, 4, 5]
res = [val for val in a if val % 2 == 0]
print(res)

Output

[2, 4]

Example 2: Here, list comprehension is used with a condition to create a new list with numbers greater than 10 from list b.

b = [5, 12, 7, 18, 3, 20]
res = [val for val in b if val > 10]
print(res)

Output

[12, 18, 20]

For Loop vs List Comprehension

For Loop

Uses multiple lines of code
Requires manual appending of elements
Better for complex logic and conditions
More readable for long operations

List Comprehension

Uses a single line of code.
Creates the list directly.
Better for simple and concise operations
More compact and faster to write

# 🐍 Python Functions: 13–19 — Scope, Arguments, Nested Functions & More

Karthick (k) — Wed, 23 Sep 2026 07:56:52 +0000

While learning Python functions, I came across several concepts that initially looked confusing. After practising them one by one, they became much easier to understand.

In this post, I’m sharing my notes and examples for:

Positional-only arguments
Keyword-only arguments
Variable scope
Local vs global variables
global
Nested functions
Returning multiple values
Functions as objects

1. Positional-Only Arguments `/`

Sometimes we want a function parameter to be passed only by position, not by its parameter name.

We can use / for this.

def student(name, age, /):
    print(name, age)

This works:

student("Karthick", 25)

But this does not:

student(name="Karthick", age=25)

Everything before / is positional-only.

Example

def calculate(a, b, /):
    return a + b

print(calculate(10, 20))

Output:

The / tells Python that a and b must be supplied positionally.

2. Keyword-Only Arguments `*`

We can also force parameters to be passed using their names.

For this, we use *.

def student(name, *, age):
    print(name, age)

This works:

student("Karthick", age=25)

But this does not:

student("Karthick", 25)

Everything after * is keyword-only.

Easy way to remember

/  → before / = positional-only

*  → after * = keyword-only

3. Variable Scope

Scope means where a variable can be accessed in a program.

For example:

def test():
    x = 10
    print(x)

test()

Here, x is available inside the function.

But:

print(x)

outside the function will cause an error because x belongs to the function's local scope.

4. Local vs Global Variables

Local Variable

A variable created inside a function is normally a local variable.

def test():
    x = 100
    print(x)

test()

Here, x is local to test().

Global Variable

A variable created outside a function is a global variable.

x = 50

def test():
    print(x)

test()

Output:

The function can access the global variable.

Easy rule

Created inside a function → Local variable

Created outside a function → Global variable

5. The `global` Keyword

What if we want to modify a global variable from inside a function?

We can use global.

x = 10

def change():
    global x
    x = 20

change()

print(x)

Output:

Without global, this:

def change():
    x = 20

would create a new local x instead of modifying the global one.

Important point

global x does not create a global variable.

It tells Python:

"Inside this function, I want to use the existing global x."

6. Nested Functions

A function defined inside another function is called a nested function.

def outer():

    def inner():
        print("Hello")

    inner()

outer()

Output:

Hello

Here:

outer()
   ↓
inner()
   ↓
Hello

The inner function can also access variables from the outer function.

def outer():
    name = "Karthick"

    def inner():
        print(name)

    inner()

outer()

Output:

Karthick

inner() doesn't have its own name, so it can access name from outer().

7. Functions Returning Multiple Values

A Python function can return multiple values.

def calculate(a, b):
    return a + b, a * b, a - b

We can store the returned values separately:

sum_value, product, difference = calculate(5, 2)

print(sum_value)
print(product)
print(difference)

Output:

7
10
3

Python actually packs the returned values into a tuple:

(7, 10, 3)

Then we unpack them:

(7, 10, 3)
 ↓   ↓   ↓
sum product difference

Important rule

The number of variables should match the number of values being unpacked.

For example:

def test():
    return 10, 20, 30

a, b, c = test()

This works.

But:

a, b = test()

causes an error because there are 3 returned values but only 2 variables.

8. Functions as Objects

One of the interesting things about Python is that functions are objects.

Consider:

def greet():
    return "Hello"

We can assign the function to another variable:

x = greet

Notice that there are no parentheses.

Now x refers to the same function.

So we can do:

print(x())

Output:

Hello

Important difference

x = greet

means:

x refers to the function itself.

Whereas:

x = greet()

means:

Call the function and store its returned value in x.

For example:

def square(n):
    return n * n

operation = square

result = operation(5)

print(result)

Output:

The flow is:

square
  ↓
function object
  ↓
operation = square
  ↓
operation(5)
  ↓
square(5)
  ↓
25

This is the foundation for passing functions to other functions.

I'm continuing my Python function learning with the next concept: passing functions to other functions.

Master Python Lists: The Only Guide You'll Ever Need 🐍

Karthick (k) — Tue, 22 Sep 2026 16:02:17 +0000

Whether you are just starting your Python journey or brushing up on your core data structures, Python lists are something you will use every single day. They are versatile, powerful, and packed with built-in features.

In this quick guide, we will cover everything from the absolute basics to some advanced tricks that will make your code cleaner and faster. Let’s dive in! 🚀

1. What is a Python List?

In Python, a list is a built-in, mutable (changeable), and ordered collection of items.

Unlike arrays in some other languages, Python lists can hold a mixture of different data types at the same time—integers, strings, floats, and even other lists!

# A simple list of strings
fruits = ["apple", "banana", "cherry"]

# A list with mixed data types
mixed_bag = [42, "Python", True, 3.14]

2. Navigating Lists: Indexing & Slicing 🗺️

Python uses zero-based indexing, meaning the first item is always at index 0. You can also use negative indexing to look at items starting from the back of the list.

Slicing Syntax: `list[start:stop:step]`

Slicing lets you extract a specific chunk of your list. Keep in mind that the stop index is exclusive (not included in the result).

numbers = [10, 20, 30, 40, 50]

print(numbers[0])   # Output: 10
print(numbers[-1])  # Output: 50 (the last item)

# Get items from index 1 up to (but not including) 4
print(numbers[1:4]) # Output: [20, 30, 40]

# Reverse a list using slicing step trick
print(numbers[::-1]) # Output: [50, 40, 30, 20, 10]

3. Essential List Methods Cheat Sheet 🛠️

Because lists are mutable, you can add, remove, and modify items on the fly. Here are the heavy hitters you need to memorize:

append(x): Adds an item to the end of the list.
insert(i, x): Inserts an item x at a specific index i.
extend(iterable): Appends all items from another list/iterable.
remove(x): Removes the first occurrence of value x.
pop(i): Removes and returns the item at index i (defaults to the last item if i is left blank).

tech_stack = ["Python", "JavaScript"]

tech_stack.append("Rust")      # ['Python', 'JavaScript', 'Rust']
tech_stack.insert(1, "HTML")   # ['Python', 'HTML', 'JavaScript', 'Rust']
tech_stack.pop()               # Removes 'Rust'

4. Next-Level Trick: List Comprehensions ⚡

If you want to write Pythonic code, you have to learn list comprehensions. They give you a short, elegant way to create new lists based on existing ones.

Instead of writing a bulky for loop like this:

squares = []
for x in range(1, 6):
    squares.append(x**2)
# Result: [1, 4, 9, 16, 25]

You can do it all in a single line:

squares = [x**2 for x in range(1, 6)]
# Result: [1, 4, 9, 16, 25]

Wrap Up 🎁

Python lists are incredibly dynamic. Master these fundamentals, play around with list comprehensions, and you will find handling data in Python becomes a breeze.

What is your favourite Python list trick? Do you prefer slicing or built-in methods? Let me know in the comments below! 👇

Pattern Problem

Karthick (k) — Mon, 21 Sep 2026 05:15:50 +0000

n=5; Here are the outputs for each of the 6 patterns provided in your blog. You can run each code snippet to see the respective output.

Pattern 1

n=5;

for i in range(n):
    for j in range(n):
        print("*",end=" ");
    print()

Output:

* * * * * 
* * * * * 
* * * * * 
* * * * * 
* * * * *

Pattern 2

n=5;

for i in range(n):
    for j in range(i+1):
        print("*",end=" ");
    print()

Output:

* 
* * 
* * * 
* * * * 
* * * * *

Pattern 3

n=5;

for i in range(1,n+1):
    for j in range(1,i+1):
        print(j,end=" ")
    print()

Output:

Pattern 4

n=5;

for i in range(1,n+1):
    for j in range(1,i+1):
        print(i,end=" ")
    print()

Output:

Pattern 5

n=5;

for i in range(n):
    for j in range(n-i):
        print("*",end=" ");
    print()

Output:

* * * * * 
* * * * 
* * * 
* * 
*

Pattern 6

n=5;

for i in range(n):
    for j in range(1,n-i+1):
        print(j,end=' ');
    print()

Output:

Feel free to copy and paste these code snippets into your Python environment to see the results yourself!

for i in range(n):
for j in range(1,n-i+1):
print(j,end=' ');
print()

React Interview Prep: Breaking Down the Core Fundamentals

Karthick (k) — Sun, 20 Sep 2026 15:34:29 +0000

Mastering technical interviews isn't about cramming the night before—it's about building a consistent daily habit. As part of my daily 75-minute interview prep routine, I break down core React concepts into concise, high-impact answers.

Here is Part 1 of the core React concepts every developer should master for technical rounds.

1. What is React?

15-Second Answer:

"React is an open-source, component-based JavaScript library used for building fast, interactive user interfaces. It uses a Virtual DOM to optimise rendering by updating only the specific parts of the real DOM that change."

Key Interview Points

View Layer ($V$ in MVC): React only handles the UI layer, giving developers full flexibility over routing and state tools.
Declarative UI: You describe what the UI should look like for a given state, and React handles the DOM updates.

2. Library vs. Framework

15-Second Answer:

"The core difference is Inversion of Control. A framework dictates your architecture and calls your code, whereas a library like React gives you full control—you call it only when you need it."

Quick Comparison

Framework (e.g., Angular, Next.js): "Don't call us, we'll call you." It provides a pre-defined blueprint and architecture.
Library (e.g., React Core): A set of specialised tools focused strictly on rendering UI.

3. Virtual DOM & Reconciliation

15-Second Answer:

"The Virtual DOM is an in-memory representation of the real DOM. When state changes, React creates a new Virtual DOM tree, compares it with the previous one using a diffing algorithm, and patches only the changed nodes in the real DOM."

Reconciliation Workflow

Price Range Slider with Min-Max Input using HTML, CSS and JavaScript

Karthick (k) — Sat, 19 Sep 2026 01:42:25 +0000

Here, we implement a Price Range Slider using HTML, CSS, and JavaScript. Users can select their desired price range by moving the slider or by manually entering minimum and maximum values. JavaScript is used to synchronise inputs and add interactivity.

HTML structures the slider and input fields.
CSS styles the slider for a clean, user-friendly UI.
JavaScript handles price updates and user interactions.

Index.html

<html>
    <head>
        <link rel="stylesheet" href="style.css">
    </head>
    <body>
        <div class="main">
            <div class="gfg">
                <p>GeeksForGeeks</p>
            </div>
            <div class="customer-wrapper">
                <div class="header">
                    <h1 class="protitle">Price Range Slider</h1>
                </div>
                <div class="price-input-container">
                    <div class="price-input">
                        <div class="price-field">
                            <span>Minimum Price</span>
                            <input type="number" class="min-input" value="2500">
                        </div>
                        <div class="price-field">
                            <span>Maximum Price</span>
                            <input type="number" class="max-input" value="8500">
                        </div>
                    </div>
                    <div class="slider">
                        <div class="price-slider"></div>
                    </div>
                </div>
                <div class="range-input">
                    <input type="range" class="min-range" min="0" max="10000" value="2500" step="1">
                    <input type="range" class="max-range" min="0" max="10000" value="8500" step="1">
                </div>
            </div>
        </div>
        <script src="script.js"></script>
    </body>
</html>

Style.css

*{
    margin: 0;
    padding:0;
}

body{
    display: flex;
    align-items: center;
    justify-content:center;
    min-height:100vh;
    background:#ffffff;
    flex-direction:column;
}

.main{
    background-color:#fff;
    border-radius:15px;
    box-shadow: 0 0 20px rgba(0, 0, 0, 0.2);
    padding:20px;
    transition:transform 0.2s;
    width:600px;
    box-sizing: border-box;
}

.main:hover{
    transform:scale(1.05);
}

.gfg{
    display: flex;
    align-items:center;
    justify-content:center;
    font-size:24px;
    font-weight:600;
    color:#01940b;
}

.customer-wrapper{
    margin: 0;
    width: 100%;
    padding: 0px 25px 40px;
    position:relative;
    box-sizing: border-box;
}
.header h1{
    font-size:30px; 
    color: #01940b;
    display:flex;
    justify-content: center;
    padding: 20px;
}

.price-input-container{
    width:100%;
}
.price-input .price-field{
    display:flex;
    margin-bottom:22px;
}

.price-field span{
    margin-right:10px;
    margin-top:6px;
    font-size:17px;
}

.price-field input{
    flex:1;
    height: 35px;
    font-size:15px;
    font-family: "DM Sans", sans-serif;
    border-radius:9px;
    text-align: center;
    border:0px;
    background:#e4e4e4;
}

.price-input{
    width:100%;
    font-size:19px;
    color:#555;
}

/* Remove Arrows/Spinners */
input::-webkit-outer-spin-button,
input::-webkit-inner-spin-button {
    -webkit-appearance: none;
    margin: 0;
}

.slider{
    width:100%;
}

.slider{
    height: 6px;
    position:relative;
    background:#e4e4e4;
    border-radius: 5px;

}

.slider .price-slider{
    height:100%;
    left:25%;
    right:15%;
    position: absolute;
    border-radius:5px;
    background:#01940b;
}

.range-input{
    position:relative;
}
.range-input input{
    position:absolute;
    width:100%;
    height:5px;
    background:none;
    top:-5px;
    pointer-events: none;
    cursor:pointer;
    -webkit-appearance: none;
    appearance: none;

}

input[type="range"]::-webkit-slider-thumb{
    height:18px;
    width:18px;
    border-radius:70%;
    background:#555;
    pointer-events:auto;
    -webkit-appearance:none;
}
@media screen and (max-width: 768px) {
    .main {
        width: 90%;
        margin-right: 5px;
    }

    .customer-wrapper {
        width: 100%;
        left: 0;
        padding: 0 10px;
    }

    .protitle {
        width: 100%;
        position: relative;

    }

    .price-input {
        display:flex;
        flex-direction: column;
        align-items: center;
    }

    .price-field {
        margin-bottom: 10px;
    }
}

Script.js

// Script.js
const rangevalue = document.querySelector(".slider .price-slider");
const rangeInputvalue = document.querySelectorAll(".range-input input");

// Set the price gap
let priceGap = 500;

// Adding event listeners to price input elements
const priceInputvalue = document.querySelectorAll(".price-input input");
for (let i = 0; i < priceInputvalue.length; i++) {
    priceInputvalue[i].addEventListener("input", e => {

        // Parse min and max values of the range input
        let minp = parseInt(priceInputvalue[0].value);
        let maxp = parseInt(priceInputvalue[1].value);
        let diff = maxp - minp

        if (minp < 0) {
            alert("minimum price cannot be less than 0");
            priceInputvalue[0].value = 0;
            minp = 0;
        }

        // Validate the input values
        if (maxp > 8000) {
            alert("maximum price cannot be greater than 10000");
            priceInputvalue[1].value = 10000;
            maxp = 10000;
        }

        if (minp > maxp - priceGap) {
            priceInputvalue[0].value = maxp - priceGap;
            minp = maxp - priceGap;

            if (minp < 0) {
                priceInputvalue[0].value = 0;
                minp = 0;
            }
        }

        // Check if the price gap is met and max price is within the range
        if (diff >= priceGap && maxp <= rangeInputvalue[1].max) {
            if (e.target.className === "min-input") {
                rangeInputvalue[0].value = minp;
                let value1 = rangeInputvalue[0].max;
                rangevalue.style.left = `${(minp / value1) * 100}%`;
            }
            else {
                rangeInputvalue[1].value = maxp;
                let value2 = rangeInputvalue[1].max;
                rangevalue.style.right = `${100 - (maxp / value2) * 100}%`;
            }
        }
    });

    // Add event listeners to range input elements
    for (let i = 0; i < rangeInputvalue.length; i++) {
        rangeInputvalue[i].addEventListener("input", e => {
            let minVal = parseInt(rangeInputvalue[0].value);
            let maxVal = parseInt(rangeInputvalue[1].value);

            let diff = maxVal - minVal

            // Check if the price gap is exceeded
            if (diff < priceGap) {

                // Check if the input is the min range input
                if (e.target.className === "min-range") {
                    rangeInputvalue[0].value = maxVal - priceGap;
                }
                else {
                    rangeInputvalue[1].value = minVal + priceGap;
                }
            }
            else {

                // Update price inputs and range progress
                priceInputvalue[0].value = minVal;
                priceInputvalue[1].value = maxVal;
                rangevalue. style.left = `${(minVal / rangeInputvalue[0].max) * 100}%`;
                rangevalue. style.right = `${100 - (maxVal / rangeInputvalue[1].max) * 100}%`;
            }
        });
    }
}

Output

Exciting Announcement: Kicking Off My New Python Project!

Karthick (k) — Fri, 18 Sep 2026 17:09:06 +0000

Hello Team and Dev Community,

I’m thrilled to share that I’m starting a new Python development project! As I wrap up the system design and architecture, I can't wait to dive deeper into the implementation phase.

In this project, I aim to leverage the latest technologies and best practices to create something truly innovative. I’m currently finalizing the user stories and synchronising our objectives, and I’m open to any feedback or suggestions you might have.

I’ll be posting regular updates on my progress on dev.to, so stay tuned for insights and lessons learned along the way. Let’s collaborate and share knowledge as we embark on this journey together!In the future, I will update you soon about the idea and all of us.

Looking forward to your thoughts and support!

DEV Community: Karthick (k)

Projects focused on Python Object-Oriented Programming (OOP) concepts.

Library Management System

Description

Features

Classes Used

How to Run

Inheritance in Python

How I Mastered React useState in One Day

Discover the Power of Python’s Built-in Functions!

List of All the Functions in Python

Strings in Python

List Comprehension in Python

# 🐍 Python Functions: 13–19 — Scope, Arguments, Nested Functions & More

1. Positional-Only Arguments /

Example

2. Keyword-Only Arguments *

Easy way to remember

3. Variable Scope

4. Local vs Global Variables

Local Variable

Global Variable

Easy rule

5. The global Keyword

Important point

6. Nested Functions

7. Functions Returning Multiple Values

Important rule

8. Functions as Objects

Important difference

Master Python Lists: The Only Guide You'll Ever Need 🐍

1. What is a Python List?

2. Navigating Lists: Indexing & Slicing 🗺️

Slicing Syntax: list[start:stop:step]

3. Essential List Methods Cheat Sheet 🛠️

4. Next-Level Trick: List Comprehensions ⚡

Wrap Up 🎁

Pattern Problem

Pattern 1

Pattern 2

Pattern 3

Pattern 4

Pattern 5

Pattern 6

React Interview Prep: Breaking Down the Core Fundamentals

1. What is React?

Key Interview Points

2. Library vs. Framework

Quick Comparison

3. Virtual DOM & Reconciliation

Reconciliation Workflow

Price Range Slider with Min-Max Input using HTML, CSS and JavaScript

Exciting Announcement: Kicking Off My New Python Project!

1. Positional-Only Arguments `/`

2. Keyword-Only Arguments `*`

5. The `global` Keyword

Slicing Syntax: `list[start:stop:step]`