Booleanization and XML Crawling

This article is inspired by the “X marks the spot” challenge in picoCTF 2021. For the solution to the challenge, skip to the ‘Exploitation’ section.

Photo by Caleb Jones on Unsplash

While SQL injections are one of the most common web application vulnerabilities, its less notorious twin can be equally, if not more dangerous.

XPath?

XPath is a query language that locates elements in an XML document. Conceptually, it is similar to SQL. Most web applications use relational databases and SQL to store and query large amounts of data. …


Board Evaluation and Minimax Algorithm

Photo by GR Stocks on Unsplash

Chess is a great game. It’s even better if you’re good at it. Regrettably, I’ve never taken the time to learn chess strategy, so I decided to rely on the power of computation and game theory instead! As a fun side project, I have implemented a simple chess AI using JavaScript.

You can find the full source code for this tutorial in my GitHub repository.


ARP scans and TCP scans with Scapy

Photo by Kaur Kristjan on Unsplash

What is Network Scanning?

Network Scanning is the process of gathering information about devices in a computer network, through employing network protocols. It is especially relevant for network administrators, penetration testers and, well… hackers.

Prerequisites

You should know basic Python. Other than that, not much! I will be writing on some basic network theory before getting into the actual code, so if you already know this stuff, feel free to skip ahead!

All code for this tutorial can be found at my GitHub repository.

Protocols, Protocols, Protocols

Communications over networks use what we call a protocol stack — building higher-level, more sophisticated conversations on top of simpler, more…


Socket programming + Tkinter GUI

Photo by Volodymyr Hryshchenko on Unsplash

I’ve recently delved into the wonderful world of computer networking. One of the fun projects I’ve created is a simple chatroom application that facilitates real-time messaging between different clients.

At any point in this tutorial, you may refer to my source code in GitHub. The aim of this tutorial is to introduce some basic networking theory while providing practical socket programming experience. If, at any point, you find that you are already comfortable with the relevant theory, please feel free to skip ahead!

Prerequisites

You should know basic Python. Other than that, nothing! In the process of creating this application, you…


A more elegant approach to doing the same thing

Photo by Maxwell Nelson on Unsplash

I’m a fan of The Zen of Python, which says

There should be one — and preferably only one — obvious way to do it.

But in Python, there are in fact many ways to achieve the same objective. Of course, some ways are more elegant than others and in most cases, it should be obvious which way is better.

We are going to look at list comprehensions, and how they can replace for loops, map() and filter() to create powerful functionality within a single line of Python code.

Basic List Comprehension

Say I want to create a list of numbers from 1…


Implementations and Explanations

We are going to look at 4 different sorting algorithms and their implementation in Python:

  • Bubble Sort
  • Selection Sort
  • Insertion Sort
  • Quicksort
Photo by Edu Grande on Unsplash

1. Bubble Sort

Time complexity: O(n²)

Implementation

def bubble(lst):
no_swaps = False
while no_swaps == False:
no_swaps = True
n = 0
for i in range(len(lst) - 1 - n):
if lst[i] > lst[i + 1]:
lst[i], lst[i + 1] = lst[i + 1], lst[i]
no_swaps = False
n += 1

How It Works

  1. Iterate through the elements in the array
  2. If there are adjacent elements in the wrong order, swap them
  3. If we have reached the end of the array and there have been no swaps in this iteration, then the array is sorted. Else, repeat from step 1.


How you can make yourself one with the Twilio API

Photo by Chris Barbalis on Unsplash

This pandemic has taken a huge toll on my mental and emotional health. In order to keep me occupied and brighten up the lives of those around me, I started on yet another Python project — this time, a WhatsApp bot that sends me random cat pictures, trending memes, the best cooking recipes, and of course, the latest world news and COVID19 statistics.

The full project can be found on my GitHub repository, and my webhook is live on https://zeyu2001.pythonanywhere.com/bot/.


Easily create, delete and switch between virtual environments.

What Is a Virtual Environment?

A virtual environment is an isolated Python environment. Working on a project in an isolated Python environment ensures that project dependencies are kept separate, and allows you to manage Python packages for different projects without breaking system tools or other projects.

For example, if both projects A and B depend on the same library, project C, but use different versions of it, Python would not be able to serve both versions of the library.

We can use virtual environments for projects A and B, and each virtual environment would be able to use their own version of project C without…

Zhang Zeyu

Simple is better than complex. Complex is better than complicated.

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