DEV Community: Sajin Joe J

python : positional argument, default argument

Sajin Joe J — Mon, 02 Nov 2026 05:02:59 +0000

In Python, positional arguments and default arguments are used when passing values to a function.
1. Positional arguments
A positional argument is passed according to the position (order) of the parameter.

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

student("Sajin", 20)

Output :

Sajin
20

Step-by-step
Parameter Argument
name "Sajin"
age 20

Python matches values based on their order.

If you change the order:

student(20, "Sajin")

Output:

20
Sajin

Here, name = 20 and age = "Sajin".

2. Default arguments
A default argument has a value assigned in the function definition.

If you don't pass a value, Python uses the default.

def login(username="admin", password="1234"):
    print(username, password)

login()

Output:

admin 1234

You can also pass your own values:

login("Sajin", "5678")

Output:

Sajin 5678

Step-by-Step:

def login(username="admin", password="1234"):
    print(username, password)

login("Sajin")

Output:

Sajin 1234

"Sajin" replaces the default username.
Password is not provided.
So Python uses the default password "1234".

3. Positional + Default arguments

def login(username, password="1234"):
    print(username, password)

login("Sajin")

Output:

Sajin 1234

Here:

username is a required positional parameter.
password is a default parameter.

You can also provide both:

login("Joe", "5678")

Output:

Joe 5678

Important rule: A parameter without a default value cannot come after a parameter with a default value.
❌ Incorrect:

def login(username="admin", password):
    print(username, password)

✅ Correct:

def login(username, password="1234"):
    print(username, password)

Operators in Python

Sajin Joe J — Tue, 27 Oct 2026 16:25:51 +0000

In Python, operators are symbols used to perform operations on variables and values.
1. Arithmetic operators
Used for mathematical calculations.

+   Addition             10 + 5      15
-   Subtraction          10 - 5      5
*   Multiplication       10 * 5      50
/   Division             10 / 5      2.0
//  Floor division       10 // 3     3
%   Modulus (remainder)  10 % 3      1
**  Power                2 ** 3      8

2. Comparison operators
Used to compare two values. The result is True or False.

==  Equal to                    5 == 5  True
!=  Not equal to                5 != 3  True
>   Greater than                5 > 3   True
<   Less than                   5 < 3   False
>=  Greater than or equal to    5 >= 5  True
<=  Less than or equal to       3 <= 5  True

Important: Python uses == for equality. It does not have JavaScript's strict equality operator ===.

3. Assignment operators
Used to assign or update values.

=     x = 10        Assign 10 to x
+=    x += 5        x = x + 5
-=    x -= 5        x = x - 5
*=    x *= 2        x = x * 2
/=    x /= 2        x = x / 2
%=    x %= 3        x = x % 3
//=  x //= 2        x = x // 2
**=  x **= 2        x = x ** 2

4. Logical operators
Used to combine conditions.

and -Both conditions must be true          5 > 2 and 8 > 3  True
or  -At least one condition must be true   5 < 2 or 8 > 3   True
not -Reverses the result                   not True         False

Example:

age = 25

if age >= 18 and age <= 60:
    print("Eligible")

Output:

Eligible

5. Membership operators
Check whether a value exists inside a sequence, such as a string or list.

in           "a" in "apple"         True
not in       "z" not in "apple"     True

Example:

fruits = ["apple", "banana", "orange"]

print("apple" in fruits)

Output:

True

Identity operators** Check whether two variables refer to the same object.

is              Same object
is not          Not the same object

a = None

print(a is None)  # True

Use is None to check whether a variable is None. Do not use is as a replacement for == when comparing ordinary values.

7. Bitwise operators
Bitwise operators in Python work on the binary representation (0s and 1s) of integers.

&   AND
\|  OR
^   XOR
~   NOT
<<  Left shift
>>  Right shift

1. Examples of bitwise operators
& — AND
Returns 1 only when both bits are 1.

a = 5   # Binary: 0101
b = 3   # Binary: 0011

print(a & b)

Output: 1

| — OR
Returns 1 when at least one bit is 1.

print(5 | 3)

Output: 7
Explanation:

  0101   (5)
| 0011   (3)
------
  0111   (7)

^ — XOR
Returns 1 when the two bits are different.

print(5 ^ 3)

Output: 6

Explanation:

  0101   (5)
^ 0011   (3)
------
  0110   (6)

~ — NOT
Reverses the bits. In Python, ~x equals -x - 1.

print(~5)

Output: -6

<< — Left shift
Shifts bits to the left. For non-negative integers, shifting left by one position multiplies the value by 2.

print(5 << 1)
print(5 << 2)

Output:

10
20

Explanation:

5  = 0101
5 << 1 = 1010  (10)
5 << 2 = 10100 (20)

>> — Right shift
Shifts bits to the right. For non-negative integers, shifting right by one position is equivalent to floor-dividing by 2.

print(5 >> 1)
print(5 >> 2)

Output:

2
1

Explanation:

5 = 0101
5 >> 1 = 0010 (2)
5 >> 2 = 0001 (1)

About Python

Sajin Joe J — Mon, 26 Oct 2026 15:50:16 +0000

Python is a beginner-friendly programming language used to build websites, automation tools, AI applications, and more. Let's learn it step by step.
1. What is Python?

Created by: Guido van Rossum.
First released: 1991.
File extension: .py
Example: hello.py

2. How to run Python on Linux Mint

Open Terminal with Ctrl + Alt + T.
Check whether Python is installed:

python3 --version

Create a Python file:

nano hello.py

Write this code in the file:

print("Hello, World!")

Save with Ctrl + O, press Enter, and exit with Ctrl + X.

Run your file:

python3 hello.py

React useState Hook

Sajin Joe J — Sun, 25 Oct 2026 15:52:33 +0000

useState is a React Hook used to store and update data in a component. When the state changes, React updates the UI.

1. Basic syntax

const [value, setValue] = useState(initialValue);

value — current state value.
setValue — function to update the state.
useState(initialValue) — sets the initial value.

2. Example: Counter

import { useState } from "react";

export default function App() {
  const [count, setCount] = useState(0);

  return (
    <div>
      <h1>{count}</h1>

      <button onClick={() => setCount(count + 1)}>
        Increment
      </button>

      <button onClick={() => setCount(count - 1)}>
        Decrement
      </button>

      <button onClick={() => setCount(0)}>
        Reset
      </button>
    </div>
  );
}

How it works:

useState(0) sets the initial count to 0.
setCount(count + 1) increases the count.
setCount(count - 1) decreases the count.
setCount(0) resets it to zero.

React JS – Complete Beginner Guide

Sajin Joe J — Sat, 24 Oct 2026 15:46:31 +0000

React is a JavaScript library used to build interactive user interfaces, especially for websites and web applications.

React helps you build websites using reusable pieces called components.

1. Install React
The easiest way to start a new React project is with Vite.
Open your terminal and run:

npm create vite@latest my-react-app
cd my-react-app
npm install
npm run dev

Choose React → JavaScript when prompted. Then open the local URL displayed in your terminal, usually http://localhost:5173/.

2.Your first React component
Create or replace the code in src/App.jsx:

function App() {
    return (
        <div>
            <h1>Hello, Sajin Joe!</h1>
            <p>Welcome to React.</p>
        </div>
    );
}

export default App;

Explanation:

function App() creates a component.
return describes what appears on the screen.
JSX lets you write HTML-like markup inside JavaScript.
export default App allows another file to import the component.

React component names normally start with a capital letter.

Callback Function in JavaScript

Sajin Joe J — Fri, 23 Oct 2026 04:05:01 +0000

A callback function is a function passed as an argument to another function so that it can be called later.

function greet(name) {
    console.log("Hello " + name);
}

function user(callback) {
    callback("Sajin Joe");
}

user(greet);

Output:

Hello Sajin Joe

Callback with a simple calculation

function calculate(a, b, callback) {
    console.log(callback(a, b));
}

function add(x, y) {
    return x + y;
}

calculate(10, 20, add);

Output:

Callback with setTimeout()

setTimeout(function() {
    console.log("Hello JavaScript");
}, 2000);

Output: Hello JavaScript after approximately 2 seconds.

The function passed to setTimeout() is a callback. The timer schedules it to run later.

Closure in JavaScript

Sajin Joe J — Thu, 22 Oct 2026 04:20:32 +0000

A closure is when an inner function remembers and can access variables from its outer function, even after the outer function has finished executing.

function outer() {
    let name = "Sajin Joe";

    function inner() {
        console.log(name);
    }

    return inner;
}

let result = outer();
result();

Output :

Sajin Joe

Synchronous, Asynchronous, and Promise in Javascript

Sajin Joe J — Thu, 15 Oct 2026 13:50:46 +0000

1. Synchronous JavaScript
Synchronous means code executes one line at a time, in order. The next line waits until the current line finishes.
Example:

console.log("First");
console.log("Second");
console.log("Third");

Output :

First
Second
Third

Explanation:

First line executes.
Then the second line executes.
Finally, the third line executes. Each statement runs in sequence.

2. Asynchronous JavaScript
Asynchronous means some operations can start and finish later, allowing other code to run while waiting.

console.log("First");

setTimeout(() => {
    console.log("Second");
}, 2000);

console.log("Third");

Output :

First
Third
Second

Explanation:

"First" prints immediately.
setTimeout() schedules the callback to run after at least 2 seconds.
"Third" prints without waiting for the timer.
"Second" prints when the timer callback run

3. What is a Promise?
A Promise is a JavaScript object that represents the eventual success or failure of an asynchronous operation.

A Promise has three states:

Pending: The operation has not finished.
Fulfilled: The operation succeeded.
Rejected: The operation failed.

Example:

let myPromise = new Promise((resolve, reject) => {
    resolve("Task completed!");
});

myPromise.then((result) => {
    console.log(result);
});

Output :

Task completed!

Explanation:

new Promise() creates a Promise.
resolve() indicates success.
.then() handles the successful result.
reject() is used to indicate failure.

Here's an example of a rejected Promise:

let myPromise = new Promise((resolve, reject) => {
    reject("Something went wrong");
});

myPromise.catch((error) => {
    console.log(error);
});

Output :

Something went wrong

JSON.stringify() and JSON.parse() in Javascript

Sajin Joe J — Wed, 14 Oct 2026 03:58:45 +0000

In JavaScript, JSON.stringify() and JSON.parse() are used to convert data between a JavaScript object and a JSON string.

1. JSON.stringify()
It converts a JavaScript object into a string.
Example :

let student = {
    name: "Sajin Joe",
    age: 25
};

let result = JSON.stringify(student);

console.log(result);
console.log(typeof result);

Output :

{"name":"Sajin Joe","age":25}
string

Explanation:

student is a JavaScript object.
JSON.stringify(student) converts the object into a string.
typeof result returns "string".

2. JSON.parse()
It converts a JSON string back into a JavaScript object.

let student = '{"name":"Sajin Joe","age":25}';

let result = JSON.parse(student);

console.log(result);
console.log(result.name);
console.log(typeof result);

Output:

{ name: 'Sajin Joe', age: 25 }
Sajin Joe
object

Explanation:

student contains JSON text as a string.
JSON.parse(student) converts it into a JavaScript object.
result.name accesses the object's name property. Remember: parse = String → Object.

3. Real-world example: Shopping cart
When using localStorage, these methods work together.

let cart = [
    { name: "Laptop", price: 50000 },
    { name: "Mouse", price: 500 }
];

// Save cart
localStorage.setItem("cart", JSON.stringify(cart));

// Get cart
let savedCart = JSON.parse(localStorage.getItem("cart"));

console.log(savedCart);

How it works:

JSON.stringify(cart) converts the cart array into a string so it can be stored.
localStorage.setItem() saves that string.
localStorage.getItem("cart") retrieves the stored string.
JSON.parse() converts the string back into an array.

Easy way to remember for interviews:

stringify → Save data.
parse → Read data back as JavaScript values.

Object Iterations in JavaScript

Sajin Joe J — Mon, 12 Oct 2026 05:44:48 +0000

Object iteration means looping through an object's properties to access its keys and values.

1. Example object

const product = {
    brand: "Samsung",
    price: 25000,
    model: "Galaxy M",
    color: "Black"
};

This object contains four properties: brand, price, model, and color

2. for...in loop
The for...in loop iterates over an object's enumerable property keys.

const product = {
    brand: "Samsung",
    price: 25000,
    model: "Galaxy M"
};

for (let key in product) {
    console.log(key);
}

Output:

brand
price
model

To get both the key and its value:

for (let key in product) {
    console.log(key, ":", product[key]);
}

Output :

brand : Samsung
price : 25000
model : Galaxy M

Remember: Use product[key] to access a property's value dynamically.
3. Object.keys()
Returns an array of the object's property names.

const product = {
    brand: "Samsung",
    price: 25000,
    model: "Galaxy M"
};

console.log(Object.keys(product));

Output:

["brand", "price", "model"]

Loop through the keys:

Object.keys(product).forEach(key => {
    console.log(key);
});

4. Object.values()
Returns an array of the object's property values.

console.log(Object.values(product));

Output:

["Samsung", 25000, "Galaxy M"]

Loop through the values:

Object.values(product).forEach(value => {
    console.log(value);
});

5. Object.entries()
Returns an array of key-value pairs. This is useful when you need both.

console.log(Object.entries(product));

Output:
[
    ["brand", "Samsung"],
    ["price", 25000],
    ["model", "Galaxy M"]
]

Using forEach():

Object.entries(product).forEach(([key, value]) => {
    console.log(key, ":", value);
});

Output :

brand : Samsung
price : 25000
model : Galaxy M

Array in JavaScript

Sajin Joe J — Fri, 09 Oct 2026 05:19:22 +0000

In JavaScript, an array is a special variable used to store multiple values in a single variable.

1. How to create an array

let fruits = ["Apple", "Mango", "Orange", "Banana"];

console.log(fruits);

Output:

["Apple", "Mango", "Orange", "Banana"]

2. Access array elements

Array indexing starts from 0, not 1.
l

let fruits = ["Apple", "Mango", "Orange", "Banana"];

console.log(fruits[0]); // Apple
console.log(fruits[1]); // Mango
console.log(fruits[2]); // Orange
console.log(fruits[3]); // Banana

3. Important array properties and methods

let fruits = ["Apple", "Mango", "Orange"];

console.log(fruits.length);

Output: 3
push() — add an element at the end

let fruits = ["Apple", "Mango"];

fruits.push("Orange");

console.log(fruits);

Output: ["Apple", "Mango", "Orange"]

pop() — remove the last element

let fruits = ["Apple", "Mango", "Orange"];

fruits.pop();

console.log(fruits);

Output: ["Apple", "Mango"]

unshift() — add an element at the beginning

let fruits = ["Mango", "Orange"];

fruits.unshift("Apple");

console.log(fruits);

Output: ["Apple", "Mango", "Orange"]

shift() — remove the first element

let fruits = ["Apple", "Mango", "Orange"];

fruits.shift();

console.log(fruits);

Output: ["Mango", "Orange"]

4. Update an array element

let fruits = ["Apple", "Mango", "Orange"];

fruits[1] = "Banana";

console.log(fruits);

Output:["Apple", "Banana", "Orange"]
The element at index 1 changes from "Mango" to "Banana".

5. Loop through an array
Use a for loop to access every element.

let fruits = ["Apple", "Mango", "Orange"];

for (let i = 0; i < fruits.length; i++) {
    console.log(fruits[i]);
}

Output :
Apple Mango Orange

forEach() — execute code for each element

let fruits = ["Apple", "Mango", "Orange"];

fruits.forEach(function(fruit) {
    console.log(fruit);
});

This prints every fruit without manually managing the index.

map()— create a new array A JavaScript Map is an object that can store collections of key-values

let numbers = [10, 20, 30, 40];

let result = numbers.map(function(num) {
    return num * 2;
});

console.log(result);

plaintext
Output : [20, 40, 60, 80]

filter() — select elements that match a condition

let numbers = [10, 15, 20, 25, 30];

let result = numbers.filter(function(num) {
    return num >= 20;
});

console.log(result);

plaintext
Output : [20, 25, 30]

9. Array of objects
This is especially useful for your JavaScript product management practice.

let products = [
    { brand: "Samsung", price: 25000 },
    { brand: "Apple", price: 50000 },
    { brand: "Vivo", price: 18000 }
];

console.log(products[0].brand); // Samsung
console.log(products[1].price); // 50000

Each array element is an object containing product information.

JavaScript Object

Sajin Joe J — Wed, 30 Sep 2026 14:56:29 +0000

An object in JavaScript is used to store related data and functionality together using key-value pairs.

1. Basic Object

const product = {
    brand: "Samsung",
    price: 25000,
    model: "MHV"
};

console.log(product);

brand, price, model → properties
"Samsung", 25000, "MHV" → values 2. Change a Property

product.price = 30000;

console.log(product.price);

Output :

3. Add a Property

product.color = "Black";

console.log(product);

Now the object has

{
    brand: "Samsung",
    price: 30000,
    model: "MHV",
    color: "Black"
}

4. Delete a Property

delete product.color;

5. Nested Object
An object can contain another object.

const product = {
    brand: "Samsung",
    price: 25000,

    port: {
        port1: "HDMI",
        port2: "AUX"
    }
};

Access nested values:

console.log(product.port.port1);
console.log(product.port.port2);