Python - Lesson 2: Setting up the environment

This lesson is an onboarding to get your computer ready before we start. It is designed for Windows, which is what we use at Core Marine, and is based on the internal introduction guide. It does not count as a class lesson: you follow it at home, with the support of the digital team, and you arrive in the classroom with everything working.

Don't rush. Half of the problems people carry for an entire course come from a poorly set up environment on day one.

Installing the tools

We are going to install two things: uv and Python.

uv is the tool that ties everything together. It installs Python for you and manages the project's dependencies without you having to fight with versions. If you come from installing Python by hand from the website, forget that path: with uv it is faster and gives fewer problems.

Once uv is installed, Python is installed with a single command, without downloading anything from the Python website:

uv python install

When you are done, check that it responds:

uv --version

If it returns a version number, you are on the right track.

Configuring VSCode for Python

We recommend VSCode as the editor. It is the most used one at Core Marine, so if you get stuck it is easier to find someone to lend you a hand. The editor comes fairly bare out of the box for Python, and this is where a lot of people stop halfway. We are going to fine-tune it.

Install the official Python extension (from Microsoft) and Pylance, which gives you autocompletion and code intelligence.
Install the Ruff extension, which warns you of problems and formats the code. It reads the configuration from the project's pyproject.toml, so the whole team formats the same way.
Select the correct interpreter: open the command palette and search for Python: Select Interpreter, and choose the one from the .venv virtual environment. The extension usually detects it on its own, but it is good to know how to do it by hand.
Enable format on save with Ruff as the default formatter. This way you stop arguing about spaces: it tidies itself up every time you save.
Configure the test panel (Test Explorer): search for Python: Configure Tests, choose pytest and the tests/ folder. From there you can run and debug the tests from the sidebar, with one click.
Get familiar with the debugger: set a breakpoint (a click in the left margin, next to the line number) and step through it. It is far more useful than filling the code with print, and we will see it in detail later, in the testing lesson.

All of this configuration lives in the project's .vscode/settings.json file, so it can be shared with the team and everyone starts the same way.

Starting a project

With the tools in place, creating a project is a matter of seconds:

uv init metocean-tools
cd metocean-tools

uv init creates the basic structure and the pyproject.toml (the project's dependency list).

Then we create and activate the virtual environment:

uv venv
.venv\Scripts\activate

A virtual environment is a folder that isolates this project's dependencies from the rest of the system. This way, if one project needs one version of a library and another needs a different one, they don't clash.

And we add dependencies when we need them. For example, a library to validate input data:

uv add msgspec

uv add downloads the library and records the exact version in pyproject.toml. That detail is gold: it means a colleague can copy your project and reproduce it without those weird "works on my machine" errors.