Unlocking the Secret World of Python List Comprehensions

Adam Gelencser
6 min readApr 23

My Wild Adventure from Clueless to Confident

Once upon a time, in the early days of my Python programming journey, I found myself struggling with what seemed like a trivial concept: list comprehensions. I had been learning Python for a few months, making decent progress, and starting to feel somewhat confident in my skills. Little did I know that my overconfidence would be my downfall when it came to list comprehensions.

Photo by Clément Hélardot on Unsplash

The Struggle Begins

It all started when I stumbled upon a line of code that looked like an alien language to me. I had just begun exploring data science and was working on a simple data manipulation task. The code snippet I encountered was:

squared_numbers = [x**2 for x in range(10)]

To my inexperienced eyes, it was as if someone had taken a list and a loop, thrown them in a blender, and hit puree. I could make out the basic ingredients, but I couldn’t understand the smoothie that came out.

I decided to try and dissect the code, attempting to break it down into its most basic components. My first guess was that it was some kind of shorthand for a loop, but my initial attempts to recreate the result using a traditional for loop were comically disastrous. I ended up with a mess of code that looked like this:

squared_numbers = []
for x in range(10):
squared_numbers = squared_numbers.append(x**2)

I spent hours trying to figure out what went wrong, not realizing that I had made a rookie mistake by trying to assign the output of the append() method to the list itself. In my frustration, I decided that list comprehensions must be some sort of sorcery that was beyond my understanding, and I tried to avoid them like the plague.

The Mysterious Coffee Shop Encounter

One day, as I was sipping my coffee and trying to solve a coding problem in a local coffee shop, a stranger approached me. They noticed that I was working on Python code and struck up a conversation about programming. As we chatted, I mentioned my struggle with list comprehensions and how they seemed like an insurmountable obstacle.

Adam Gelencser

Tech enthusiast, currently entrepreneuring — regularly sharing content on tech news and irregularly on other topics. Founder of QMapper.co video AI tool.