How Software Actually Runs

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The Problem

Let’s start with something that seems simple but isn’t.

You write code. A Python script, let’s say. Just 20 lines. It reads a CSV file and prints a summary.

You run it on your laptop.

It works.

So far, so good.

Now your colleague asks you to send it to them. They want to run the same script on their machine.

You send the file. They double-click. And…

ModuleNotFoundError: No module named 'pandas'

Okay, they need to install pandas. They do. They try again.

Python 3.11 is required. You have Python 3.8.

They update Python. Other things on their machine break because they depended on Python 3.8.

Here’s the thing.

Your code didn’t just run. It ran inside an environment. And that environment is invisible until it’s wrong.