Forem: Abu Hurayra

Understanding PHP Types – Booleans

Abu Hurayra — Mon, 21 Oct 2024 02:00:00 +0000

What is a Boolean?

In PHP, a Boolean is a data type that can have only two values:

true: Represents a positive or affirmative state.
false: Represents a negative or false state.

Boolean values are often used in conditional statements, comparisons, and logical operations. It is important to note that both true and false are case-insensitive. So, true, True, truE, TRUE are all valid.

Creating Boolean Variables

You can create a Boolean variable by assigning the values true or false directly:

Example:

<?php
$isAvailable = true;  // Boolean variable set to true
$isLoggedIn = false;  // Boolean variable set to false

var_dump($isAvailable); // Output: bool(true)
var_dump($isLoggedIn);  // Output: bool(false)
?>

The var_dump() function is used here to display the type and value of the variables.

Boolean Conversion

In PHP, many data types can be converted to Boolean. A value can be type casted into boolean using (bool). Generally this is not necessary because when a value is used in a logical context it will be automatically interpreted as a value of type bool.

When converting to boolean, the following values will return false:

the boolean false itself
the integer value 0
the float values 0.0 and -0.0
empty string, ""
string with a single zero, "0"
an empty array
the type null
variables that are unset
some other complex values

All other values are considered true, including resource and NAN.

Example:

<?php
$values = [0, 1, "", "Hello", [], [1, 2, 3], null, 0.0, 3.14];
foreach ($values as $value) {
    var_dump((bool)$value);
}
?>

Output:


bool(false) // 0
bool(true) // 1
bool(false) // ""
bool(true) // "Hello"
bool(false) // []
bool(true) // [1, 2, 3]
bool(false) // null
bool(false) // 0.0
bool(true) // 3.14

Using Booleans in Conditional Statements

Booleans are primarily used in conditional statements such as if, else, and switch to control the flow of the program.

Example:

<?php
$isUserLoggedIn = true;

if ($isUserLoggedIn) {
    echo "Welcome, User!"; // This message will be displayed
} else {
    echo "Please log in.";
}
?>

In this example, since $isUserLoggedIn is true, the message “Welcome, User!” will be displayed.

Comparison Operators and Booleans

PHP provides various comparison operators that return Boolean values:

Equality (==): Checks if values are equal.
Identity (===): Checks if values and types are identical.
Inequality (!= or <>): Checks if values are not equal.
Non-identity (!==): Checks if values or types are not identical.
Greater than (>) and Less than (<): Used for numeric comparisons.

Example:

<?php
$a = 10;
$b = "10";

var_dump($a == $b);   // Output: bool(true)  - values are equal
var_dump($a === $b);  // Output: bool(false) - types are different
var_dump($a > 5);     // Output: bool(true)  - 10 is greater than 5
var_dump($a != 10);   // Output: bool(false) - 10 is equal to 10
?>

Logical Operators and Booleans

Logical operators are used to combine or negate Boolean expressions:

&& (AND): Returns true if both operands are true.
|| (OR): Returns true if at least one operand is true.
! (NOT): Negates a Boolean expression.

Example:

<?php
$isMember = true;
$hasPaid = false;

if ($isMember && $hasPaid) {
    echo "Access granted.";  // Will not be executed
} else {
    echo "Access denied.";   // Output: Access denied.
}

$isAdmin = !$isMember;
var_dump($isAdmin);  // Output: bool(false) - negates true to false
?>

Some Boolean Caveats

1. Loose Comparisons

Using == can lead to unexpected results due to type juggling. Always use === for strict comparisons.

Example:

<?php
var_dump(0 == false);  // Output: bool(true)
var_dump(0 === false); // Output: bool(false)
?>

In the first case, 0 and false are considered equal because 0 converts to false when compared loosely.

2. Falsy Values

Certain values like 0, "0", and empty arrays are considered false, which can sometimes lead to logical errors.

Example:

<?php
$var = "0";

if ($var) {
    echo "True";  // This will not be displayed
} else {
    echo "False"; // Output: False
}
?>

3. Short-Circuit Evaluation

Logical operators && and || use short-circuit evaluation. This means if the result is determined by the first operand, the second operand is not evaluated.

Example:

<?php
$x = false && foo(); // foo() will not be called because $x is false
$y = true || foo();  // foo() will not be called because $y is true
?>

4. Case Sensitivity

true and false are case-insensitive, so True, FALSE, and fAlSe are valid but not recommended for consistency.

Understanding PHP Types - NULL

Abu Hurayra — Sun, 20 Oct 2024 10:18:41 +0000

Introduction

The null type in PHP represents a variable with no value assigned to it. It is a special data type used to indicate the absence of a value or to explicitly state that a variable is empty. Understanding how null works and how to use it effectively is essential for managing variables and handling conditions in PHP.

What is `null` in PHP?

In PHP, a variable is considered null if:

It has been assigned the constant null.
It has not been assigned any value.
It has been unset using the unset() function.

Example:

<?php
$var1 = null;  // Assigned null value explicitly
$var2;         // No value assigned
unset($var3);  // Variable has been unset

var_dump($var1); // Output: NULL
var_dump($var2); // Output: NULL
var_dump($var3); // Output: NULL
?>

Characteristics of the `null` Type

null is case-insensitive, so null, NULL, and NuLl are all treated the same.
It is the only possible value of the null type.
The is_null() function can be used to check whether a variable is null.

Checking for null Values

To check if a variable is null, you can use the is_null() function or a strict comparison with ===.

Example using is_null():

<?php
$var = null;

if (is_null($var)) {
    echo "The variable is null.";
}
?>

Example using strict comparison (===):

<?php
$var = null;

if ($var === null) {
    echo "The variable is null.";
}
?>

Default `null` Values

If a variable is declared but not assigned a value, PHP automatically assigns it the null type.

Example:

<?php
$var;  // Declared but not assigned a value
var_dump($var);  // Output: NULL
?>

Unsetting Variables

The unset() function is used to destroy a variable. After calling unset(), the variable becomes null.

Example:

<?php
$var = 10;
unset($var);

var_dump($var);  // Output: NULL
?>

Using `null` in Conditional Statements

null is treated as false in boolean contexts. This means you can use null in if statements to check whether a variable is empty.

Example:

<?php
$var = null;

if (!$var) {
    echo "The variable is null or false.";
}
?>

Setting Default Values Using `null` Coalescing Operator (`??`)

PHP 7 introduced the null coalescing operator (??), which allows you to check if a variable is null and provide a default value if it is.

Example:

<?php
$username = null;

// If $username is null, use "Guest" as the default value
echo $username ?? "Guest";  // Output: Guest
?>

This is especially useful when working with user inputs or configurations that may not always be set.

Common Use Cases for `null` in PHP

Initializing Variables

Use null to explicitly initialize variables when you do not yet have a value for them.

$response = null;  // Will be assigned a value later

Resetting Values

Use null to reset a variable’s value, indicating that it no longer holds any data.

$user_data = getUserData();
$user_data = null;  // Free up memory

Optional Parameters in Functions

Use null as a default value for optional parameters in functions.

function greet($name = null) {
    if ($name === null) {
        echo "Hello, Guest!";
    } else {
        echo "Hello, $name!";
    }
}

greet();         // Output: Hello, Guest!
greet("John");   // Output: Hello, John!

Conclusion

The null type in PHP is a fundamental concept that signifies the absence of a value. It is versatile and can be used to initialize variables, check for empty states, and handle optional parameters. Understanding how to work with null will help you write more robust and error-resistant code. Whether you’re checking for unset variables or using the null coalescing operator, mastering the null type is an essential part of becoming proficient in PHP development.

Understanding Comments in PHP

Abu Hurayra — Sat, 19 Oct 2024 02:00:00 +0000

Like any other programming languages, PHP supports different types of comments. Though comments are ignored by the PHP interpreter, they are essential for developer experience (DX). Let’s learn more about comments in PHP.

Types of Comments in PHP

PHP supports three types of comments:

1. Single Line Comments

Single-line comments are used to comment out a single line or part of a line in your code. You can use either // or # to denote a single-line comment.

Example:

<?php
// This is a single-line comment using double slashes.

echo "Hello, World!"; // This comment is at the end of a line.

# This is another way to write a single-line comment using a hash.
?>

2. Multi-line Comments

Multi-line comments, also known as block comments, are used to comment out multiple lines of code. They start with /* and end with */. This type of comment is useful when you need to temporarily disable large blocks of code or write longer explanations.

Example:

<?php
/* 
   This is a multi-line comment.
   It can span multiple lines.
   It is useful for commenting out large sections of code.
*/
echo "This line will be executed.";

?>

3. Documentation Comments

Documentation comments are a specialized form of multi-line comments. They start with /** and are often used to generate documentation using tools like PHPDoc. This type of comment is typically placed above functions, classes, or methods to describe their purpose, parameters, and return values.

Example:

<?php
/**
 * Adds two numbers together.
 *
 * @param int $a The first number.
 * @param int $b The second number.
 * @return int The sum of the two numbers.
 */
function add($a, $b) {
    return $a + $b;
}

echo add(3, 4); // Outputs: 7
?>

The @param and @return annotations provide metadata that can be used by documentation generators to produce well-structured and detailed documentation.

Best Practices for Using Comments

Keep Comments Relevant and Up-to-Date: Outdated comments can be more confusing than no comments at all. Always update your comments when you change the code.
Avoid Obvious Comments: Comments like // Increment by 1 above a line of code like $i++; are unnecessary. Comments should add value by explaining why the code does something, not what it does.
Use Documentation Comments for Functions and Classes: This helps you and others understand what the function or class does, what parameters it accepts, and what it returns.
Use Comments to Explain Complex Logic: If your code contains complex logic or algorithms, use comments to break it down and explain the reasoning behind your approach.

<?php

//======================================================================
// CATEGORY LARGE FONT
//======================================================================

//-----------------------------------------------------
// Sub-Category Smaller Font
//-----------------------------------------------------

/* Title Here Notice the First Letters are Capitalized */

# Option 1
# Option 2
# Option 3

/*
 * This is a detailed explanation
 * of something that should require
 * several paragraphs of information.
 */

// This is a single line quote.
?>

How to Edit php.ini Files

Abu Hurayra — Fri, 18 Oct 2024 02:00:00 +0000

Intro

PHP configurations are managed through the php.ini file. Editing this file allows you to customize various PHP settings such as enabling or disabling short tags, setting memory limits, and more.

This guide will show you how to edit the php.ini file on Ubuntu servers for both OpenLiteSpeed and Nginx to enable short PHP tags.

Locating `php.ini` File for Nginx on ubuntu

Depending on the PHP version you are using, the php.ini file is typically located in one of the following directories:


/etc/php/7.4/fpm/php.ini  # For PHP 7.4
/etc/php/8.0/fpm/php.ini  # For PHP 8.0
/etc/php/8.1/fpm/php.ini  # For PHP 8.1

We can use the command php --ini in the terminal to find the path of the php.ini file.

root@ubuntu:~# php --ini
Configuration File (php.ini) Path: /etc/php/8.1/cli
Loaded Configuration File:         /etc/php/8.1/cli/php.ini
Scan for additional .ini files in: /etc/php/8.1/cli/conf.d
Additional .ini files parsed:      /etc/php/8.1/cli/conf.d/10-mysqlnd.ini,
.... .... ....

To find the exact path, run:

php --ini | grep "Loaded Configuration File"

This is the output:

root@ubuntu:~# php --ini | grep "Loaded Configuration File"
Loaded Configuration File:         /etc/php/8.1/cli/php.ini

Locating `php.ini` File for OpenLiteSpeed on ubuntu

For OpenLiteSpeed, the php.ini file is usually located in:

/usr/local/lsws/lsphp74/etc/php/7.4/litespeed/php.ini  # For PHP 7.4
/usr/local/lsws/lsphp80/etc/php/8.0/litespeed/php.ini  # For PHP 8.0

If you’re unsure of the path, you can find it by running:

php --ini | grep "Loaded Configuration File"

This is the output:

root@ubuntu:~# php --ini | grep "Loaded Configuration File"
Loaded Configuration File:         /usr/local/lsws/lsphp81/etc/php/8.1/litespeed/php.ini

Editing the `php.ini` File

Use a text editor like nano or vim to open the php.ini file. Replace 8.1 with your actual PHP version.

For Nginx:

nano /etc/php/8.1/cli/php.ini

For OpenLiteSpeed:

nano /usr/local/lsws/lsphp81/etc/php/8.1/litespeed/php.ini

Search for the short_open_tag directive. To search in nano, press Ctrl + W, type short_open_tag, and press Enter.

Modify the line to:

short_open_tag = On

If the line is commented out (has a ; at the beginning), remove the ; to uncomment it.

For nano, press Ctrl + X, then Y, and press Enter to save and exit.
For vim, press Esc, type :wq, and press Enter.

Restart Services To Apply Changes

After making the changes, we need to restart the services to apply the changes.

For Nginx:

sudo systemctl restart php8.1-fpm
sudo systemctl restart nginx

For OpenLiteSpeed:

sudo systemctl restart lsws

Verify The Changes

To confirm that the short tags are enabled, create a test PHP file in your web server’s root directory:

<?  // Notice how we are using short tags.
    phpinfo(); 
?>

Access this file via your browser (e.g., http://yourserver.com/test.php). Check the short_open_tag value in the output to see if it is set to On.

Conclusion

Editing the php.ini file is straightforward but requires attention to detail. Always ensure you have the correct path to the php.ini file and restart the appropriate services after making changes. This guide covered how to enable short PHP tags for both Nginx and OpenLiteSpeed on Ubuntu servers.

PHP Tags

Abu Hurayra — Thu, 17 Oct 2024 11:00:00 +0000

In PHP there are several types of tags that can be used to embed PHP code within HTML or other documents. Let’s go over each of them, their differences, supported versions, and how to enable or disable them.

Standard PHP Tags

This is the syntax of standard PHP tags:

<?php
    echo "Bismillah!";
?>

Supported Version: PHP 4 and later.
Always enabled by default, can not be disabled.
Recommended to use.

Short Open Tags (`<? ... ?>`)

These are a shorthand of the standard PHP tags. This is the syntax:

<?
    echo "Alhamdulillah";
?>

Supported Version: PHP 3 and later
Can be enabled or dsiabled by the short_open_tag directive in php.ini
- To Enable: short_open_tag = On
- To Disable: short_open_tag = Off
Not recommended to use because these can conflict with XML declarations.

Short Echo Tags (`<?= ... ?>`)

These are a shorthand for <?php echo ... ?>

<?= $message; ?>

Supported version: PHP 5.4 and later
Enable/Disable: Always enabled in PHP 5.4 and later, regardless of the short_open_tag directive.
Use these for output but make sure that the server has them enabled.

ASP Style Tags (`<% ... %>`)

These tags are similar to ASP or JSP style tags:

<%
    echo "Assalamu Alaikum";
%>

Supported Version: PHP 3 to PHP 7.0
Can be enabled or disabled by the asp_tags directive in php.ini (removed as of PHP 7.0)
- Enable: asp_tags = On
- Disable: asp_tags = Off
These are no longer supported in the modern versions of PHP.

Script Tags

This syntax allows you to embed PHP code in HTML like a script block.

<script language="php">
    echo "This is a script tag.";
</script>

Supported version: PHP 3 and later.
These are always enabled but rarely used in modern applications. Not supported in XHTML and newer versions of HTML.

Python Input/Output for Competitive Programming

Abu Hurayra — Wed, 26 Apr 2023 03:53:29 +0000

Python has become one of the most popular languages to use for algorithmic problem solving and competitive programming. Despite having some downsides due to its slower speed, its popularity is increasing due to the simplicity of python syntax and easier learning curve.

In this post, we will learn how to take input and print output for various competitive programming problems.

Example - 01

Problem Link: 1352C. K-th Not Divisible by n

The problem statement says that the first line will contain one integer t. Then there will be t lines. Each line will have 2 integers, n and k.

We can at first take t as input, then run a loop. In each turn of the loop, we can take n and k.

The output is a single number for each n and k. We can use the print() function to print the output.

Here is the code:

t = int(input())

for i in range(t):

    n, k = map(int, input().split())

    # Solve the problem here

    # Write output here
    print(solution)

This is the complete solution to the problem:

import math

t = int(input())

for i in range(t):

    n, k = map(int, input().split())

    solution = k + math.floor((k-1)/(n-1))

    print(solution)

Example - 02

Problem Link: 1352C. K-th Not Divisible by n

WP-CLI Example Guide

Abu Hurayra — Wed, 26 Apr 2023 03:52:47 +0000

What is wp-cli?

WP-CLI is the command line interface for WordPress.
It is an extensible tool for installing and maintaining WordPress.
Everything you can do from a browser, can also be done using the wp-cli.

In this guide we will learn some useful commands and create scripts to automate some common tasks.

Here are some of the most useful commands:

wp plugin update --all Update all plugins that can be updated.
wp db export Export the database an an SQL dump.
wp checksum core Verifies the integrity of the WordPress core and makes sure that the core files have not been tampered with.
wp plugin install user-switching --activate Install and activate a wordpress plugin.
wp transient delete --all Delete transient data.

Let's automate some common tasks using wp-cli:

User Create/Update/Delete/Generate:

Create an editor named bob with the email bob@example.com and password b0bp@s52@0#2$3

wp user create bob bob@example.com --role=editor --user_pass=b0bp@s52@0#2$3

Generate 100 subscribers

wp user generate --count=100 --role=subscriber

Data Structures in Python: list()

Abu Hurayra — Fri, 11 Feb 2022 04:50:58 +0000

Arrays are one of the most fundamental data structures. Python does not have built-in support for arrays, but python lists can be used instead.

Characteristics

Python lists have the following characteristics:

Lists are ordered. Items in a list have a defined order and the order will not change. Inserted items are placed at the end.
List items are changeable. Items can be modified, added or removed.
Lists allow duplicates. It can contain the same value multiple times.
List items can be accessed using indexes.

Time Complexities For Different List Methods

Operation	Average Case	Amortized Worst Case
Copy	O(n)	O(n)
Append[1]	O(1)	O(1)
Pop last	O(1)	O(1)
Pop intermediate[2]	O(n)	O(n)
Insert	O(n)	O(n)
Get Item	O(1)	O(1)
Set Item	O(1)	O(1)
Delete Item	O(n)	O(n)
Iteration	O(n)	O(n)
Get Slice	O(k)	O(k)
Del Slice	O(n)	O(n)
Set Slice	O(k+n)	O(k+n)
Extend[1]	O(k)	O(k)
Sort	O(n log n)	O(n log n)
Multiply	O(nk)	O(nk)
x in s	O(n)
min(s), max(s)	O(n)
Get Length	O(1)	O(1)

Now let's look at the list methods and how to use them:

append()

This method adds an element at the end of the list.

a = [1, 2, 4, 7]
a.append(8)
print(a)
# Output: [1, 2, 4, 7, 8]

clear()

Removes all the elements from the list.

a = [1, 2, 4, 7]
a.clear()
print(a)
# Output: []

copy()

Returns a copy of the list.

a = [1, 2, 4, 7]
x = a.copy()
print(x)
# Output: [1, 2, 4, 7]

count()

Returns the number of elements with the specified value.

a = [1, 0, 1, 1, 0, 0, 1]
countOnes = a.count(1)
print(countOnes)
# Output: 4

extend()

Add the elements of a list (or any iterable), to the end of the current list. It only takes one argument.

a = [1, 0, 2]
b = ['cat', 'dog', 2]
a.extend(b)
print(a)
# Output: [1, 0, 2, 'cat', 'dog', 2]

index()

Returns the index of the first element with the specified value. If the specified value does not exist in the list, then a ValueError is raised.

a = [1, 0, 2, 'cat', 'dog', 2]
k = a.index('cat')
print(k)
# Output: 3

insert()

This method takes a position and a value and inserts the value at the specified position.

a = [1, 0, 2, 'cat', 'dog', 2]
# Insert 'orange' at the index 1
a.insert(1, 'orange')
print(a)
# Output: [1, 'orange', 0, 2, 'cat', 'dog', 2]

pop()

Removes the element at the specified position. If no argument is passed then the last element is removed from the list and returned.

a = [1, 0, 3, 'cat', 'dog', 2]
x = a.pop()
print(x)
# Output: 2
print(a)
# Output: [1, 0, 3, 'cat', 'dog']

But if an index is passed as argument, then the item at that position is removed and returned.

a = [1, 0, 3, 'cat', 'dog', 2]
x = a.pop(3)
print(x)
# Output: cat
print(a)
# Output: [1, 0, 3, 'dog', 2]

remove()

Removes the first item with the specified value. But if the specified value does not exist in the list then a ValueError is raised.

a = [1, 0, 7, 'cat', 'dog', 7]
a.remove(7)
print(a)
# Output: [1, 0, 'cat', 'dog', 7]

reverse()

This method reverses the order of the list.

a = [1, 0, 7, 'cat', 'dog', 7]
a.reverse()
print(a)
# Output: [7, 'dog', 'cat', 7, 0, 1]

sort()

This method sorts the list. By default the sorting is done in ascending order (small to large).

a = [1, 0, 7, 3, 5, 7]
a.sort()
print(a)
# Output: [0, 1, 3, 5, 7, 7]

The sort() method can accept two arguments reverse and key.

The reverse argument can be True or False.
reverse=True will sort the list in descending order. (large to small)

a = [1, 0, 7, 3, 5, 7]
a.sort(reverse=True)
print(a)
# Output: [7, 7, 5, 3, 1, 0]

The key argument however, accepts a function. For example, if I have a list of strings and I want to sort them according to their lengths, I can do the following:

a = ['cat', 'mouse', 'hare', 'elephant']
a.sort(key=len)
print(a)
# Output: ['cat', 'hare', 'mouse', 'elephant']

However, the next example is more interesting and can help us in a lot of scenarios.

Suppose you have a list of dictionaries. The dictionaries each contain the name and age of a person. You want to sort the dictionaries according to the age values. You can do this:

# This function returns the age value
def myFunc(d):
    return d['age']

a = [
        {'name':'Abu Hurayra', 'age': 23},
        {'name':'Obayed', 'age': 27},
        {'name':'Shariful Islam', 'age': 25},
        {'name':'Khairul Islam', 'age': 14}
]

a.sort(key=myFunc)

print(a)
# Output: [
#    {'name': 'Khairul Islam', 'age': 14}, 
#    {'name': 'Abu Hurayra', 'age': 23}, 
#    {'name': 'Shariful Islam', 'age': 25}, 
#    {'name': 'Obayed', 'age': 27}
#    ]

References:

Data Structures in Python: set()

Abu Hurayra — Thu, 10 Feb 2022 15:13:10 +0000

Do you remember what a Set is from your school days? A set is a well-defined group of distinct objects.

A set can be a very useful tool for computer programming. Python has a built-in set type. In this article we will learn about the set data type in python, its operations, complexities and where we can use this type.

What Are The Characteristics Of A Set In Python?

Python set has these characteristics:

Set items are unique. A set can not contain duplicate values or objects.
Sets are unordered. Set items do not follow any particular ordering. So we can not access set items with indexes like we can with arrays.
Set items can not be modified, but they can be removed and inserted.

How Do I Create A Set In Python?

We can create a set in python in the following ways:

a = set()
b = {1, 2, 3, 4}
c = set([1, 2, 3, 4])

What are the time complexities of common set operations?

Insertion: O(1) on average. But worst case can cause O(n) due to collision.
Searching: O(1) on average. But worst case can cause O(n) due to collision.

Operation	Average case	Worst Case	notes
x in s	O(1)	O(n)
Union s\	t	O(len(s)+len(t))
Intersection s&t	O(min(len(s), len(t))	O(len(s) * len(t))	replace "min" with "max" if t is not a set
Multiple intersection s1&s2&..&sn		(n-1)*O(l) where l is max(len(s1),..,len(sn))
Difference s-t	O(len(s))
s.difference_update(t)	O(len(t))
Symmetric Difference s^t	O(len(s))	O(len(s) * len(t))
s.symmetric_difference_update(t)	O(len(t))	O(len(t) * len(s))

What Methods Can Be Used With Sets?

A Set supports these methods:

add()

Adds an element to the set. If the element we are trying to add already exists in the set, then nothing will change.

clear()

Removes all the elements from the set.

copy()

Returns a copy of the set.

difference()

Returns a set containing the difference between two or more sets. It means which elements of the first set are not present in the second set.

difference_update()

Removes the items in the first set that are also included in the second set.

discard()

Remove the specified item. If the item is not present in the set, then nothing will happen. No error will be shown.

intersection()

Returns a set, that is the intersection of two or more sets. It means which elements are common to all of the given sets.

intersection_update()

Removes the items in this set that are not present in other, specified set(s). Which means that only the common items will be kept in the first set and other items will be removed.

isdisjoint()

Returns whether two sets have an intersection or not. Are the two sets completely different?

issubset()

Returns if the first set a subset of the second or not.

issuperset()

Returns whether the first set is a superset of the second set or not.

pop()

Removes and returns a random element from the set. If the set is empty, then an error occurs.

remove()

Removes the specified element. An error will be raised if the item to remove does not exist. Use discard() instead of remove() to avoid the error.

symmetric_difference()

Returns a set with the symmetric differences of two sets. Symmetric difference means the set of all items except those that are common in both sets.

symmetric_difference_update()

Update the first set with the symmetric difference if the 2 sets.

union()

Return a set containing the union of sets.

update()

Update the set with another set, or any other iterable.

When is a set useful?

A set allows us to insert and search for elements in O(1) time on average. This is due to the underlying hash table that implements a python set. The uniqueness of the elements can be used to efficiently remove duplicates from a list.

Thank you so much for reading

☺

References:

Deletion From a Simple Linked List Using Python

Abu Hurayra — Thu, 02 Sep 2021 16:37:23 +0000

Deleting a node from a linked list is straightforward but there are a few cases we need to account for:

1. The list is empty
2. The node to remove is the only node in the linked list
3. We are removing the head node
4. We are removing the tail node
5. The node to remove is somewhere in between the head and tail node
6. The item to remove does not exist in the linked list.

Step 1: If the list is empty then print a message and return.

def delete(self, key):
    # If the list is empty
    if self.head is None:
        print('Deletion Error: The list is empty.')
        return

Step 2: If the head holds the key, delete the head by assigning head to the next node of head.

    # If the key is in head
    if self.head.data == key:
        self.head = self.head.next
        return

Step 3: Find the first occurrence of the key in the linked list.

    # Find position of first occurrence of the key
    current = self.head
    while current:
        if current.data == key:
            break
        previous = current
        current = current.next

If the key was found then point the previous node to the next node of the key. Otherwise print an error message.

    # If the key was not found
    if current is None:
        print('Deletion Error: Key not found.') 
    else:
        previous.next = current.next

Step 4: Check sample test cases for the code.

The complete code is given below:

class Node:
    def __init__(self, data):
        self.data = data 
        self.next = None

class LinkedList:
    def __init__(self):
        self.head = None

    def printList(self):
        temp = self.head
        if not temp:
            print('List is empty.')
            return
        else:
            print('Start:', end=' ')
        while temp:
            print(temp.data, end=' -> ')
            temp = temp.next
        print('end.')

    def insert(self, data):
        new_node = Node(data)

        # If the linked list is empty
        if self.head is None:
            self.head = new_node

        # If the data is smaller than the head
        elif self.head.data >= new_node.data:
            new_node.next = self.head
            self.head = new_node

        else:
            # Locate the node before the insertion point
            current = self.head
            while current.next and new_node.data > current.next.data:
                current = current.next

            # Insertion
            new_node.next = current.next
            current.next = new_node

    def delete(self, key):
        # If the list is empty
        if self.head is None:
            print('Deletion Error: The list is empty.')
            return 

        # If the key is in head
        if self.head.data == key:
            self.head = self.head.next
            return

        # Find position of first occurrence of the key
        current = self.head
        while current:
            if current.data == key:
                break
            previous = current
            current = current.next

        # If the key was not found
        if current is None:
            print('Deletion Error: Key not found.') 
        else:
            previous.next = current.next



if __name__=='__main__':
    # Create an object
    LL = LinkedList()
    print('')

    # Insert some nodes
    LL.insert(10)
    LL.insert(12)
    LL.insert(8)
    LL.insert(11)
    LL.insert(10)


    LL.printList()
    LL.delete(7)
    LL.delete(8)
    LL.delete(13)
    LL.printList()

Thank you for reading the article. Please leave you feedback. 😄

References:

https://www.geeksforgeeks.org/linked-list-set-3-deleting-node/
CLRS: Introduction to Algorithms [book]

Insertion in a Sorted Linked List Using Python

Abu Hurayra — Thu, 02 Sep 2021 12:19:09 +0000

Insertion in a sorted linked list can have 3 outcomes:

If the given data is the smallest then it will be inserted at the beginning.
If the data is the biggest then it will be inserted at the end of the list.
Otherwise it will be inserted where the next node data bigger than the given data.

Step 1: Create a new node with the data

    def insert(self, data):
        new_node = Node(data)

Step 2: If the linked list is empty then insert the node at the head

        # If the linked list is empty
        if self.head is None:
            self.head = new_node

Step 3: If the data is smaller than the head, insert it at the beginning

        # If the data is smaller than the head
        elif self.head.data >= new_node.data:
            new_node.next = self.head
            self.head = new_node

Step 4: Locate the node that is the biggest node smaller than the given node and insert the node after it.

            # Locate the node before the insertion point
            current = self.head
            while current.next and new_node.data > current.next.data:
                current = current.next

            # Insertion
            new_node.next = current.next
            current.next = new_node

This is how the insert function will look:

    def insert(self, data):
        new_node = Node(data)

        # If the linked list is empty
        if self.head is None:
            self.head = new_node

        # If the data is smaller than the head
        elif self.head.data >= new_node.data:
            new_node.next = self.head
            self.head = new_node

        else:
            # Locate the node before the insertion point
            current = self.head
            while current.next and new_node.data > current.next.data:
                current = current.next

            # Insertion
            new_node.next = current.next
            current.next = new_node

Step 5: Write a print method to print the linked list:

    def printList(self):
        temp = self.head
        if not temp:
            print('List is empty.')
            return
        else:
            print('Start:', end=' ')
        while temp:
            print(temp.data, end=' -> ')
            temp = temp.next
        print('end.')

Write some code to test the output:

if __name__=='__main__':
    LL = LinkedList()
    LL.printList()

    LL.insert(10)
    LL.insert(12)
    LL.insert(8)
    LL.insert(11)
    LL.insert(10)


    LL.printList()

This is how the output looks:

The complete program:

class Node:
    def __init__(self, data):
        self.data = data 
        self.next = None

class LinkedList:
    def __init__(self):
        self.head = None

    def printList(self):
        temp = self.head
        if not temp:
            print('List is empty.')
            return
        else:
            print('Start:', end=' ')
        while temp:
            print(temp.data, end=' -> ')
            temp = temp.next
        print('end.')

    def insert(self, data):
        new_node = Node(data)

        # If the linked list is empty
        if self.head is None:
            self.head = new_node

        # If the data is smaller than the head
        elif self.head.data >= new_node.data:
            new_node.next = self.head
            self.head = new_node

        else:
            # Locate the node before the insertion point
            current = self.head
            while current.next and new_node.data > current.next.data:
                current = current.next

            # Insertion
            new_node.next = current.next
            current.next = new_node


if __name__=='__main__':
    # Create an object
    LL = LinkedList()
    # Print Empty List
    LL.printList()
    # Insert some nodes
    LL.insert(10)
    LL.insert(12)
    LL.insert(8)
    LL.insert(11)
    LL.insert(10)
    # Print the list
    LL.printList()

Thank you for reading the article. 😄

References:

Create a Simple Linked List Using Python

Abu Hurayra — Wed, 01 Sep 2021 12:01:28 +0000

Step 1: Create a Node Class

Every linked list has nodes that are linked together to form a linked list. A node contains a data and a link. The link is used to store the address of the next element in the list.

Let's create a Node class in python:

class Node:
    def __init__(self, data):
        self.data = data 
        self.next = None

Step 2: Create a Linked List Class

A linked list class will contain the head of the linked lists and other methods like insert, delete and search.

Let's create a LinkedList class in python:

class LinkedList:
    def __init__(self):
        self.head = None

Step 3: Create a Linked List

In order to create a linked list, we need to create an object from the LinkedList class.

LL = LinkedList()

Now let's create 3 nodes with values 10, 11 and 12. The first node is the head.

LL.head = Node(10)
second = Node(11)
third = Node(12)

Link all the nodes together: head will point to second and second will point to third. The third node points to None which is already set.

LL.head.next = second
second.next = third

Step 4: Create a Method to Print the list

Let's add a printList() method to the LinkedList class. This method will take the head node and print the values while traversing the node until it reaches the end.

class LinkedList:
    def __init__(self):
        self.head = None

    def printList(self):
        temp = self.head
        while temp:
            print(temp.data)
            temp = temp.next

We have to call the printList() method in order to print the linked list.

LL.printList()

This is how the output will look:

10
11
12

The complete python program:

class Node:
    def __init__(self, data):
        self.data = data 
        self.next = None

class LinkedList:
    def __init__(self):
        self.head = None

    def printList(self):
        temp = self.head
        while temp:
            print(temp.data)
            temp = temp.next


LL = LinkedList()

LL.head = Node(1)
second = Node(2)
third = Node(3)

LL.head.next = second
second.next = third

LL.printList()

Thanks for reading the post 😄

References:

https://www.geeksforgeeks.org/linked-list-set-1-introduction/

Forem: Abu Hurayra

Understanding PHP Types – Booleans

What is a Boolean?

Creating Boolean Variables

Boolean Conversion

Using Booleans in Conditional Statements

Comparison Operators and Booleans

Logical Operators and Booleans

Some Boolean Caveats

1. Loose Comparisons

2. Falsy Values

3. Short-Circuit Evaluation

4. Case Sensitivity

Understanding PHP Types - NULL

Introduction

What is null in PHP?

Characteristics of the null Type

Checking for null Values

Default null Values

Unsetting Variables

Using null in Conditional Statements

Setting Default Values Using null Coalescing Operator (??)

Common Use Cases for null in PHP

Initializing Variables

Resetting Values

Optional Parameters in Functions

Conclusion

Understanding Comments in PHP

Types of Comments in PHP

1. Single Line Comments

2. Multi-line Comments

3. Documentation Comments

Best Practices for Using Comments

How to Edit php.ini Files

Intro

Locating php.ini File for Nginx on ubuntu

Locating php.ini File for OpenLiteSpeed on ubuntu

Editing the php.ini File

Restart Services To Apply Changes

Verify The Changes

Conclusion

PHP Tags

Standard PHP Tags

Short Open Tags (<? ... ?>)

Short Echo Tags (<?= ... ?>)

ASP Style Tags (<% ... %>)

Script Tags

Python Input/Output for Competitive Programming

Example - 01

Example - 02

WP-CLI Example Guide

What is wp-cli?

Here are some of the most useful commands:

User Create/Update/Delete/Generate:

Data Structures in Python: list()

Characteristics

Time Complexities For Different List Methods

append()

clear()

copy()

count()

extend()

index()

insert()

pop()

remove()

reverse()

sort()

Data Structures in Python: set()

What Are The Characteristics Of A Set In Python?

How Do I Create A Set In Python?

What are the time complexities of common set operations?

What Methods Can Be Used With Sets?

add()

clear()

copy()

difference()

difference_update()

discard()

intersection()

What is `null` in PHP?

Characteristics of the `null` Type

Default `null` Values

Using `null` in Conditional Statements

Setting Default Values Using `null` Coalescing Operator (`??`)

Common Use Cases for `null` in PHP

Locating `php.ini` File for Nginx on ubuntu

Locating `php.ini` File for OpenLiteSpeed on ubuntu

Editing the `php.ini` File

Short Open Tags (`<? ... ?>`)

Short Echo Tags (`<?= ... ?>`)

ASP Style Tags (`<% ... %>`)