DEV Community: Keerthana M

python Tuples

Keerthana M — Tue, 29 Sep 2026 14:34:29 +0000

basket = {'apple', 'orange', 'apple', 'pear', 'orange', 'banana'}
print(basket) # show that duplicates have been removed

'orange' in basket # fast membership testing

'crabgrass' in basket

Demonstrate set operations on unique letters from two words

a = set('abracadabra')
b = set('alacazam')
a # unique letters in a

a - b # letters in a but not in b

a | b # letters in a or b or both

a & b # letters in both a and b

a ^ b # letters in a or b but not both

s = {'Hi', 10,20,True}

s.remove('Hello')
print(s)

s.discard('Hello')
print(s)

tel = {'jack': 4098, 'sape': 4139}
tel['guido'] = 4127
tel['guido'] = 4127
print(tel)
tel['guido'] = 4199
print(tel)

Variable in java

Keerthana M — Mon, 28 Sep 2026 16:04:53 +0000

VARIABLES:

In Java there are two types of variable
Global Variable

-> Static Variable
-> Non-Static Varible

Local Variable

Static variable:

A static variable in Java is a class-level variable that is declared using the static keyword
Static variable is used to store the class information.
Unlike instance variables, only one copy of a static variable is created and shared among all objects of the class, making it useful for storing common data.

Public class Super{
Static string name="Murugan";
Static int addno=108;
public static void main(String[] args){
System.out.println(Super.name);
System.out.println(Super.addno);
}
}

Output:
Murugan 108

Static variables take single memory space for the whole class

OBJECT:

In Java Object is a instance of a class
It represents a specific entity created from the class template.

Public class Super{
Static string name="Murugan";
String pro_name="Laptop";
int price=25000;
Static int addno=108;
public static void main(String[] args){
Super product=new Super();   ---------------> This is the object creation 
System.out.println(Super.name);
System.out.println(Super.addno);
}
}

In Object creation it will allocate the space for the some product in the supermarket
Object is a Non- Static Information used to store the object information
What is field ?
In java field is a global variable
if we assign variable in the main method is a local variable otherwise it is a global variable
In java we doesnot assign any value for the variable means it will take a default value as 0
String=null int=0 double=0.0 boolean=false
example:

Public class Super{
Static string name= "Murugan"
string pro-name;
int addno;
Public Static void main (String[] args){
Super product1=new Super();
Super product2=new Super();
product1.pro_name="Boost";
product1.price=250;
product2.pro_name="soap";
product2.price=300;
}
}

Output:
Boost 250 soap 300

When we create a object means it will take one memory space if we create another object means it will take another memory space.
so non-static variabes are the object information
Static variables are the class information

Java Interview questions.

Keerthana M — Mon, 28 Sep 2026 16:04:23 +0000

Question1:

Why java?

python [LIST]

Keerthana M — Sat, 26 Sep 2026 06:47:45 +0000

1) Find max, second max from a given list

l1 = [100,28,46,78]
max = l1[0]
for i in l1:
    if i > max:
        max = i
print(max)
l1 = [28,46,78,100]
max = l1[0]
second_max = 0
for i in l1:
    if i >= max:
        second_max = max
        max = i
print(second_max)

Output:
100 78

2) Find min, second min from a given list

l1 = [100,28,46,78]
min = l1[0]
for i in l1:
    if i <= min:
        min = i
print(min)
l1 = [100,46,78,28]
min = l1[0]
second_min = 0
for i in l1:
    if i <= min:
        second_min = min
        min = i
print(second_min)

Output:
28 46

3) Reverse a list without using reverse()

l1 = [100,28,48,69]
rev = []
i = len(l1)-1
while i>=0:
    rev.append(l1[i])
    i-=1
print(rev)

Output:
[69, 48, 28, 100]

4) Confirm if a given list is palindrome or not:

l1 = [10,20,30,20,10]
l2 = l1[::-1]
print(l1==l2)

Output:
True

5) Remove duplicate elements from a list:

l1 = [10,20,30,20,10]
l2 = []
for i in l1:
    if i not in l2:
        l2.append(i)
print(l2)

Output:
[10,20,30]

python patterns {Alphabets}

Keerthana M — Thu, 24 Sep 2026 12:36:56 +0000

To print A

for row in range (1,8):
    for col in range(1,8):
        if  col==1 or col== 7 or row == 1 or row == 4  :
            if (row==1 and(col==1 or col==7)) or (row==7 and (col==1 or col==7)):
                print(" ", end=' ')
            else:
                print("*", end=' ') 
        else:
            print(" ", end=' ')
    print()

To print B

for row in range (1,8):
    for col in range(1,8):
        if  row==1 or row== 7 or row==4 or col == 1 or col == 7  :
            if (row==1 and  col==7) or (row==7 and  col==7):
                print(" ", end=' ')
            else:
                print("*", end=' ') 
        else:
            print(" ", end=' ')
    print()

To print C

for row in range (1,8):
    for col in range(1,8):
        if  row==1 or row == 7 or col == 1:
            if (row==1 and(col==1 or col==7)) or (row==7 and (col==1 or col==7)):
                print(" ", end=' ')
            else:
                print("*", end=' ') 
        else:
            print(" ", end=' ')
    print()

To print D

for row in range (1,8):
    for col in range(1,8):
        if  row==1 or row== 7 or col == 3 or col == 7  :
            if (row==1 and(col==1 or col==7)) or (row==7 and (col==1 or col==7)):
                print(" ", end=' ')
            else:
                print("*", end=' ') 
        else:
            print(" ", end=' ')
    print()

To print E

for row in range (1,8):
    for col in range(1,8):
        if  row==1 or row== 7 or row==4 or col == 1:
                print("*", end=' ') 
        else:
            print(" ", end=' ')
    print()

To print F

for row in range (1,8):
    for col in range(1,8):
        if  row==1 or row==4 or col == 1:
                print("*", end=' ') 
        else:
            print(" ", end=' ')
    print()

To print H

for row in range (1,8):
    for col in range(1,8):
        if   row==4 or col == 1 or col == 7:
                print("*", end=' ') 
        else:
            print(" ", end=' ')
    print()

To print I

for row in range (1,8):
    for col in range(1,8):
        if   col==4 or row == 1 or row == 7:
                print("*", end=' ') 
        else:
            print(" ", end=' ')
    print()

To print J

for row in range (1,8):
    for col in range(1,8):
        if   col==4 or row == 1 or row == 7:
             if   (col==4 and row == 7) or(row==7 and col==5) or (row==7 and col==6 ) or (row==7 and col==7):
                print(" ", end=' ')
             else:
                print("*", end=' ') 
        else:
            print(" ", end=' ')
    print()

To print L

for row in range (1,8):
    for col in range(1,8):
        if   col==1 or row == 7 :
                print("*", end=' ') 
        else:
            print(" ", end=' ')
    print()

To print T

for row in range (1,8):
    for col in range(1,8):
        if   col==4 or row == 1 :
                print("*", end=' ') 
        else:
            print(" ", end=' ')
    print()

Data Types

Keerthana M — Wed, 23 Sep 2026 06:35:29 +0000

DATATYPE:

byte --> 1byte
short --> 2byte
int --> 4byte
long --> 8byte
float --> 4byte
double--> 8byte
char()--> can store single letter in a single quotes('A')
boolean--> True or False

Variable Declaration:

int mark = 100;
Boolean variable = true;

public class  Home {
static String name = "Ragul";             // class information
Static int age =25                        // class information
}

static refferes to class specific Information.

java Features

Keerthana M — Wed, 23 Sep 2026 06:21:24 +0000

EXAMPLE PROGRAM:

public class Home{
public static void ( String args[]){
    System.out.println("hello");
}
}

OUTPUT:
hello

Java Features:

OBJECT ORIENTED PROGRAMMING LANGUAGE:

OOPS in Java refers to Object-Oriented Programming System, which is built on four main principles:

Encapsulation,
Inheritance,
Polymorphism,
Abstraction.

These concepts help Java create modular, reusable, and maintainable applications.
OOPS (Object-Oriented Programming System) is a programming paradigm centered around objects that contain data (fields) and behavior (methods).
Java is inherently object‑oriented and uses OOPS to structure programs efficiently.

OOPS Concepts in Java

1. Class

A class is a blueprint for creating objects. It defines attributes and methods. Example: Car is a class; BMW is an object.

2. Object

An object is an instance of a class.
It has:
State (data)
Behavior (methods)
Identity (unique memory reference)

3. Encapsulation

Binding data and methods together while restricting direct access using access modifiers.
Achieved using private fields and getter/setter methods.

4. Inheritance

Allows one class to acquire properties and behaviors of another class.
Promotes code reusability.

5. Polymorphism

Ability of a method or object to take many forms.
Compile-time polymorphism: Method overloading
Runtime polymorphism: Method overriding

6. Abstraction

Hiding internal implementation details and showing only essential features.
Achieved using abstract classes and interfaces.

CLASS:

Class is a container. (Blueprint, template.) Syntax:

Class Home{
   .......
   .......
}

Class name must be meaningful.
Class name should start with uppaercase.

class Home{
public static void main (String[] args){
System.out.println("HELLO WORLD!!!!");
}
}

{Home, System, string} are class in func.
No space between Class name.
Eg: play ground
can use {$, _}
No special char allowed (except:$,_)
Number are allowed at mid or end of Class.
Not at the beginning of the classname.

class Home{
Static string name ="payilagam";
Static int addno=108;
//static keyword is used to store the class information is common for all and it take 1 memory space for whole class
public static void main(String[] args){
System.out.println(Home.name);
System.out.println(Home.age);
}
}

java errors finding.

Keerthana M — Tue, 22 Sep 2026 05:53:18 +0000

Task1: Making errors and finding the name of the error:

 public class Home{
 public static void main( String args){
     System.out.println("hello");
 }
 }

output:
error: can't find main(String[]) or main() method in class: Home

public class Home{

public static void main( String args[){
    System.out.println("hello");
}
}

output:
Home.java:3: error: ']' expected
public static void main( String args[){
^
1 error
error: compilation failed

public class Home{

public static void main( String []){
    System.out.println("hello");
}
}

output:
Home.java:3: error: expected
public static void main( String []){
^
1 error
error: compilation failed

public class Home{

public static void main( String args[]{
     System.out.println("hello");
}
}

output:
Home.java:3: error: ',', ')', or '[' expected
public static void main( String args[]{
^
1 error
error: compilation failed

public class Home{

public static void main( String args[]){
     System.println("hello");
}
}

output:
Home.java:4: error: cannot find symbol
System.println("hello");
^
symbol: method println(String)
location: class System
1 error
error: compilation failed

public class Home{

public static void main( String args[]){
     System.OUT.println("hello");
}
}

output:
Home.java:4: error: cannot find symbol
System.OUT.println("hello");
^
symbol: variable OUT
location: class System
1 error
error: compilation failed

public class Home{

public static void main( String args[]){
     System.out.println("hello");
}

output:
Home.java:5: error: reached end of file while parsing
}
^
1 error
error: compilation failed

public class Home{

public static void main(string args[]){
     System.out.println("hello");
}
}

output:
Home.java:3: error: cannot find symbol
public static void main(string args[]){
^
symbol: class string
location: class Home

public class Home{

public static void main( String args[]){
     system.out.println("hello");
}
}

output:
Home.java:4: error: package system does not exist
system.out.println("hello");
^
1 error
error: compilation failed

public class Home{

public static  main( String args[]){
    System.out.println("hello");
}
}

output:
Home.java:3: error: invalid method declaration; return type required
public static main( String args[]){
^
1 error
error: compilation failed

public class Home{

public static void ( String args[]){
    System.out.println("hello");
}
}

output:
Home.java:3: error: expected
public static void ( String args[]){
^
1 error
error: compilation failed

public  Home{

public static void main( String args[]){
    System.out.println("hello");
}
}

output:
Home.java:1: error: class, interface, annotation type, enum, record, method or field expected
public Home{
^
Home.java:6: error: class, interface, annotation type, enum, record, method or field expected
}
^
2 errors
error: compilation failed

INTRODUTION OF Java

Keerthana M — Mon, 21 Sep 2026 16:03:42 +0000

INTRODUTION OF Java:

Java is an High level programming language.
Java is also known as compiler programming language.
It is Statically data type(stric conditons)

When java was invented?
The project began in June 1991,The language was initially called "Oak".
It was later renamed to "Java" in 1995.Java was designed by James Gosling at Sun Microsystems.
Java 1.0, was released on January 23, 1996.
Java SE 17: Released on September 14, 2021.(latest version of java)

why java?

In C++ the programming was difficult in multiple platforms, And it has platform dependency.
To over come this situation, Java has been invented. Java is know for faster efficiency.

JAVA ARCHITECTURE:

JDK (Java Development Kit) is the complete package for Java development. It includes:

JRE (Java Runtime Environment)

Development tools like javac (compiler), javadoc, jar, and debuggers. Developers use JDK to write, compile, and debug Java programs.
It is platform-dependent, with separate builds for Windows, Linux, and macOS.

JRE (Java Runtime Environment) is meant for running Java applications. It contains:

JVM (Java Virtual Machine)

Core libraries and supporting files. It cannot compile code; it only provides the runtime environment to execute precompiled bytecode.
JVM (Java Virtual Machine) is the execution engine that converts Java bytecode into machine-specific instructions. Key responsibilities:

Class loading (via ClassLoader)
Bytecode verification for security
Execution (interpretation or JIT compilation)

Memory management and garbage collection JVM is platform-dependent in implementation but executes platform-independent bytecode.

JIT (Just-In-Time Compiler) is a component of the JVM designed to improve performance.

Instead of interpreting all bytecode, JIT compiles frequently used bytecode sequences into native machine code at runtime, caching them for reuse. Optimizations include:
Register allocation
Eliminating redundant expressions
Reducing memory access This results in faster execution while maintaining JVM’s portability and safety.

How to create and execute java file:

Example:

public class Home{

public static void main( String args[]){
     System.out.println("hello");
 }
}

OUTPUT:

hello

React useRef and useparams

Keerthana M — Mon, 21 Sep 2026 07:33:20 +0000

React useRef Hook:

The useRef Hook allows you to persist values between renders.
It can be used to store a mutable value that does not cause a re-render when updated.
It can be used to access a DOM element directly.
If we tried to count how many times our application renders using the useState Hook, we would be caught in an infinite loop since this Hook itself causes a re-render.
To avoid this, we can use the useRef Hook.

syntax:

const myRef = useRef(0);

You can read or update this value at any time using myRef.current.

Two Main Use Cases:

Direct DOM Manipulation:

DOM manipulation allows developers to interact with and modify the structure, style, and content of web pages.
In this article, we'll explore the fundamentals of DOM manipulation in JavaScript, breaking down complex concepts into easy-to-understand snippets.

import { useRef } from 'react';

function FocusInput() {
  const inputRef = useRef(null); // 1. Create the ref box

  const handleClick = () => {
    // 3. Access the DOM node directly and focus it
    inputRef.current.focus(); 
  };

  return (
    <>
      {/* 2. Link the ref box to the HTML input element */}
      <input ref={inputRef} type="text" />
      <button onClick={handleClick}>Focus the input</button>
    </>
  );
}

2.Storing Data That Shouldn't Cause Re-Renders:

Use useRef to store values that persist across renders without triggering re-renders. This allows you to track values or DOM elements without affecting the rendering cycle.
Avoid using useState for data that should not change frequently. Instead, use useRef for tracking values that persist across multiple renders.

import { useRef } from 'react';

function Timer() {
  const timerIdRef = useRef(null);

  const startTimer = () => {
    // Storing the interval ID without forcing a re-render
    timerIdRef.current = setInterval(() => {
      console.log('Tick');
    }, 1000);
  };

  const stopTimer = () => {
    // Clearing the interval using the stored ID
    clearInterval(timerIdRef.current);
  };

  return (
    <div>
      <button onClick={startTimer}>Start</button>
      <button onClick={stopTimer}>Stop</button>
    </div>
  );
}

useParams:

The useParams hook in React Router allows you to access the dynamic parameters from the current URL.
This is particularly useful for handling routes with dynamic segments.

Syntax

const { param1, param2, ... } = useParams();

param1, param2, etc., are route parameters defined in the path.
UseParams returns an object where keys are the parameter names and values are the values from the URL.

Extracts URL data:

It returns an object containing key-value pairs of the dynamic segments defined in your route path.

Dynamic rendering:

You can use these extracted values to fetch specific data or display user-specific information on your webpage

example:
1. Define the Route with a Colon (:):

In your routing setup, you mark the dynamic parts of your URL path using a colon (:) followed by a variable name.

import { BrowserRouter, Routes, Route } from "react-router-dom";
import UserProfile from "./UserProfile";

function App() {
  return (
    <BrowserRouter>
      <Routes>
        {/* ':id' is the dynamic parameter here */}
        <Route path="/user/:id" element={<UserProfile />} />
      </Routes>
    </BrowserRouter>
  );
}

2. Extract the Parameter inside the Component:

If a user visits /user/42 or /user/santhosh, you use useParams() inside that component to grab that specific value.

import { useParams } from "react-router-dom";

function UserProfile() {
  // Destructure the 'id' parameter directly from useParams()
  const { id } = useParams(); 

  return (
    <div>
      <h2>User Profile</h2>
      <p>The current User ID is: <strong>{id}</strong></p>
    </div>
  );
}

export default UserProfile;

PYTHON - STRING MANIPULATION

Keerthana M — Mon, 21 Sep 2026 05:57:12 +0000

1. ANAGRAM:

The word1 and word2 must contain same length.
The word1 and word2 must contain the same letters in the both words.

#act - cat, race - care, listen - silent

word1 = input("Enter word: ") #cat 
word2 = input("Enter word: ") #act 

if len(word1) != len(word2):
print("Not anagram")
else:
for letter in word1: #cat
if word1.count(letter) != word2.count(letter):
print('Not anagram')
break 
else:
print('Anagram')

Output:
Enter word: cat Enter word: act Anagram

2. ROTATION:

word = 'abcd' 
for i in range(len(word)):
    rotate = word[1:]+word[0]
    word = rotate
    print(rotate)

Output:
bcda cdab dabc abcd

3. Shortest word in a sencentence.

import sys
sen = 'chief minister vijay returned from uk'
lst = sen.split(' ')
min_len = sys.maxsize 
shortest_word = ''
for i in lst:
if len(i)<min_len:
min_len = len(i)
shortest_word = i
print('Shortest word is ',shortest_word)

OUTPUT:
Shortest word is uk

4. Duplicate letters count and The most frequent letter

word = 'keertisadana'
lst = list(word)
max_count = 0
most_frequent = ' '
i = 0
while i < len (lst):
key = lst[i]
count = 1
j = i+1
while j<len(lst):
if key == lst[j] and key != '*':
lst[j] = '*'
count+=1
j+=1
if key != '*' and count > max_count:
max_count = count
most_frequent = key
i+=1
print(f"The most frequent letter is '{most_frequent}' appearing {max_count} times.")

OUTPUT:

['k', 'e', 'e', 'r', 't', 'i', 's', 'a', 'd', 'a', 'n', 'a'] e is present 2 times a is present 3 times Duplicate Letters Count is 2

5.Password Validator:

1) Length 8 letters
2) Capital Letter
3) Number
4) Special Character !@#$%^&*()_;:'"<>?

isupper()
islower()
isdigit()

upper = 0
lower = 0
digit = 0
special = 0
password = input("Enter Password: ")
for letter in password:
if letter.isupper():
upper +=1
elif letter.islower():
lower +=1
elif letter.isdigit():
digit+=1
else:
special+=1

if len(password) >= 8 and upper>0 and lower > 0 and special > 0:
print('Valid Password')
else:
print("invalid Password')

OUTPUT:
Enter Password:P@yil123 Valid Password

6. password generator

import random
import string

length = int(input("enter password length:"))

letters = string.ascii_lowercase + string.ascii_uppercase + string.digits

password = ""
for i in range(length):
    password = password + random.choice(letters)
print(password)

output:
enter password length:8
P@yil123

React [Reactmemo and Usememo]

Keerthana M — Fri, 18 Sep 2026 05:44:25 +0000

ReactMemo

Using memo will cause React to skip rendering a component if its props have not changed.
This can improve performance.

Problem

The Todos component re-renders even when the todos have not changed.
When you click the increment button, the Todos component re-renders.
If this component was complex, it could cause performance issues.

Solution:

To fix this, we can use memo.
Use memo to keep the Todos component from needlessly re-rendering.
The Todos component only re-renders when the todos that are passed to it through props are updated.