Polars Open Source Sprint: Fix Your First Issue or Build Your Own Expression Plugin
What is an open source sprint?
An open source sprint is an event where programmers come together to make focused contributions to an open source project within a limited timeframe. Participants can work individually or in groups, collaborate directly on coding tasks, fix bugs, and develop new features for the project. The sprint environment offers hands-on coding, mentorship from experienced contributors, and fosters networking and community building among peers. Through time-boxed sessions, programmers can learn from each other, solve problems collaboratively, and quickly advance project goals in a welcoming, supportive setting.
Why should you join?
- Gain practical coding experience on real-world projects
- Receive guidance and mentorship from skilled contributors
- Make a meaningful impact on an open source project
- Expand your professional network and meet like-minded peers
- Learn best practices and new technologies in a supportive environment
Specifically: A hands-on sprint for people who use Polars and want to go one layer deeper. Pick one of two tracks: work on a "good first issue" from the Polars issue tracker, or build an expression plugin that adds your own custom functionality to Polars, running at native speed. You leave with either an open PR or a working plugin, and a setup you can keep using afterwards.
Polars is developed in the open, but the step from user to contributor can be big: a Rust codebase, build times, and unfamiliar conventions. This sprint removes that friction by putting you in a room with the people who build Polars.
You choose one of two tracks at the start.
Track 1: Good first issues. We walk through the repository layout, the build and test workflow, and how a change moves from issue to merged PR. Then you pick an issue labelled "good first issue" (Python API, documentation, or Rust, depending on your comfort) and work on it with review and guidance during the session.
Track 2: Expression plugins. Polars lets you register your own expressions written in Rust and call them from Python like any built-in. We start from a template, build a small plugin end to end, and then you extend it with functionality relevant to your own work: a domain-specific string parser, a custom aggregation, a distance metric, whatever Polars is missing for you.
What you will learn:
- How the Polars codebase and contribution workflow are organised
- How to build Polars from source and run the test suite
- How the expression plugin system works and when it beats map_elements or a UDF
- How to scaffold, compile, and call a plugin from Python
Outline:
- Intro: how Polars is developed, how plugins fit into the expression engine (15 min)
- Track kickoff: pick an issue, or scaffold a plugin (15 min)
- Sprint: hands-on work with support from the Polars team (75 min)
- Wrap-up: voluntary show and tell, open PRs, next steps (15 min)
Prerequisites (please do these before the session; the first Polars build takes 20+ minutes and Wi-Fi is shared):
- Laptop with a GitHub account, git, and a recent Python installed
- Rust toolchain via rustup (https://rustup.rs)
- Track 1: fork and clone https://github.com/pola-rs/polars, follow the build steps in the contributing guide (https://docs.pola.rs/development/contributing), and confirm that importing your local build works
- Track 2: install maturin, and generate a project from the Polars plugin cookiecutter template (https://github.com/MarcoGorelli/cookiecutter-polars-plugins); the accompanying plugin tutorial is a useful read beforehand
- Optional: browse the "good first issue" label on the Polars repo and shortlist one or two you find interesting
A setup checklist and links will be shared in a GitHub repo ahead of the session.
Thijs Nieuwdorp is the DevRel Engineer at Polars in Amsterdam. His interest in the interaction between human and computer led him to an education in Artificial Intelligence at the Radboud University, after which he dove straight into the field of Data Science. At Xomnia he witnessed the birth of Polars as Ritchie Vink started working on it during his employment there , and has been using it in his projects ever since. Outside work Thijs enjoys exploring our world through hiking and traveling, and exploring other worlds through books, games, and movies.
Ritchie Vink is the creator of Polars and CEO of Polars Inc. He started the project in 2020 and has led its design and development since, from the query engine and expression API to the plugin system attendees will use in this sprint.