Contributing

As an open source project, Mesa welcomes contributions of many forms, and from beginners to experts. If you are curious or just want to see what is happening, we post our development session agendas and development session notes on Mesa discussions. We also have a threaded discussion forum on Matrix for casual conversation.

In no particular order, examples include:

Code patches
Bug reports and patch reviews
New features
Documentation improvements
Tutorials

No contribution is too small. Although, contributions can be too big, so let's discuss via Matrix OR via an issue.

To submit a contribution

Create a ticket for the item that you are working on.
Fork the Mesa repository.
Clone your repository from Github to your machine.
Create a new branch in your fork: git checkout -b BRANCH_NAME
Run git config pull.rebase true. This prevents messy merge commits when updating your branch on top of Mesa main branch.
Install an editable version with developer requirements locally: pip install -e ".[dev]"
Edit the code. Save.
Git add the new files and files with changes: git add FILE_NAME
Git commit your changes with a meaningful message: git commit -m "Fix issue X"
If implementing a new feature, include some documentation in docs folder.
Make sure that your submission works with a few of the examples in the examples repository. If adding a new feature to mesa, please illustrate usage by implementing it in an example.
Make sure that your submission passes the GH Actions build. See "Testing and Standards below" to be able to run these locally.
Make sure that your code is formatted according to [the black] standard (you can do it via pre-commit).
Push your changes to your fork on Github: git push origin NAME_OF_BRANCH.
Create a pull request.
Describe the change w/ ticket number(s) that the code fixes.
Format your commit message as per Tim Pope's guideline.

I have no idea where to start

That's fine! Here's a rough outline where you could start, depending on your experience:

I'm a modeller (but not an experienced developer)

You already know how to build Mesa models (if not skip below), and probably have found things Mesa can't do (elegantly). You want to improve that. Awesome!

First step is to install some proper tools, if you haven't already.

A good IDE helps for code development, testing and formatting. PyCharm or VSCode for example.
Dive into Git and GitHub. Watch some videos, this takes some time to click. GitHub Desktop is great.
https://github.dev/projectmesa/mesa is great for small changes (to docs).

Learn the tools, talk to us about what you want to change, and open a small PR. Or update an example model (check open issues)!

I'm a developer (but not a modeller)

Awesome! You have the basics of open-source software development (if not check above), but not much modelling experience.

First step is to start thinking like a modeller. To understand the fine details about our library and contribute meaningfully, get some modelling experience:

Go though our series of introductory tutorials at Getting Started. While going through them, dive into the source code to really see what everything does.
Follow an ABM course (if possible). They might be a bit outdated programming language wise, but conceptual they're sound.
- This MOOC on ABM concepts: Agent Based Modeling
- This MOOC on practical ABM modelling: Agent-Based Models with Python: An Introduction to Mesa
Go though multiple of our examples. Play with them, modify things and get a feel for Mesa and ABMs.
- Check our open issues for the examples.
- If you see anything you want to improve, feel free to open a (small) PR!
If you have a feel for Mesa, check our discussions and issues.
- Also go thought our release notes to see what we recently have been working on, and see some examples of successful PRs.
Once you found or thought of a nice idea, comment on the issue/discussion (or open a new one) and get to work!

I'm both

That's great! You can just start working on things, reach out to us. Skim to the list above if you feel you're missing anything. Start small but don't be afraid to dream big!

I'm neither

Start with creating your own models, for fun. Once you have some experience, move to the topics above.

Testing and Code Standards

:target: https://codecov.io/gh/projectmesa/mesa

:target: https://github.com/psf/black

As part of our contribution process, we practice continuous integration and use GH Actions to help enforce best practices.

If you're changing previous Mesa features, please make sure of the following:

Your changes pass the current tests.
Your changes pass our style standards.
Your changes don't break the models or your changes include updated models.
Additional features or rewrites of current features are accompanied by tests.
New features are demonstrated in a model, so folks can understand more easily.

To ensure that your submission will not break the build, you will need to install Ruff and pytest.

pip install ruff pytest pytest-cov

We test by implementing simple models and through traditional unit tests in the tests/ folder. The following only covers unit tests coverage. Ensure that your test coverage has not gone down. If it has and you need help, we will offer advice on how to structure tests for the contribution.

py.test --cov=mesa tests/

With respect to code standards, we follow PEP8 and the Google Style Guide. We use [ruff format] (a more performant alternative to black) as an automated code formatter. You can automatically format your code using pre-commit, which will prevent git commit of unstyled code and will automatically apply black style so you can immediately re-run git commit. To set up pre-commit run the following commands:

pip install pre-commit
pre-commit install

You should no longer have to worry about code formatting. If still in doubt you may run the following command. If the command generates errors, fix all errors that are returned.

ruff check . --fix

Licensing

The license of this project is located in LICENSE. By submitting a contribution to this project, you are agreeing that your contribution will be released under the terms of this license.

Roles in Mesa

Mesa has several roles to help structure our collaboration and recognize great work. They also form a progression path for community members to that want to take on increasing responsibility in the project. Since we're all volunteers, everyone contributes what they can when they can - there are no minimum time commitments. Also, the best ideas and contributions can come from anyone, these roles are just a way to coordinate our efforts.

Feel free to reach out to us anytime to discuss your interests and ambitions in the project. We're always happy to chat about how you can grow your involvement in Mesa!

Contributor

Contributors help improve Mesa through:

Code contributions
Documentation improvements
Bug reports and fixes
Example models
Tutorial improvements
Answering questions
Participating in discussions
Testing pre-releases
Sharing Mesa with others

Everyone can contribute what they can, when they can. No contribution is too small! Contributors who have a PR successfully merged receive the "Contributor" label on GitHub.

Collaborator

When contributors consistently demonstrate technical skills and community mindset through their contributions, they may be invited to become collaborators. Collaborators help coordinate by:

Reviewing pull requests
Triaging issues and discussions
Coordinating between contributors
Leading specific areas of development
Helping new contributors
Participating in project planning
Building community

The collaborator role recognizes people who help Mesa grow through both their technical contributions and community involvement. Collaborators receive GitHub triage permissions and the "Collaborator" label.

Maintainer

Maintainers help guide Mesa's overall development while ensuring the project remains sustainable and welcoming. They focus on:

Project vision and roadmap
Major architectural decisions
Release management
Community governance
Mentoring collaborators
Setting community standards
Long-term sustainability

Maintainers are selected based on their technical expertise, project understanding, and community leadership. Maintainers receive full repository permissions and the "Member" label.

Special Roles

In some cases, special roles may be created for specific purposes, such as leading particular initiatives or components within Mesa. These roles are created as needed based on project requirements and may come with specific permissions and labels.

All roles are expected to:

Follow Mesa's code of conduct
Communicate respectfully
Work collaboratively
Help maintain a welcoming community
Make decisions transparently

Mesa grows through good ideas and contributions. We're all volunteers working together to make Mesa better. Don't hesitate to reach out to any maintainer to discuss your interests and potential growth within the project!

Maintainers' notes

Some notes useful for Mesa maintainers.

Releases

To create a new release, follow these steps:

Ensure all pull requests (PRs) have a clear title and are labeled with at least one label. Check this link to see if all PRs are labeled. These labels will be used when drafting the changelog using the .github/release.yml configuration.
Navigate to the Releases section in the GitHub UI and click the Draft a new release button.
Specify the upcoming tag in the Choose a tag and Release title fields (e.g., v3.0.0).
- For pre-releases, add a a, b or rc and a number behind the version tag (see Versioning), and check the box Set as a pre-release.
Use the Generate release notes button to automatically create release notes. Review them carefully for accuracy, and update labels and edit PR titles if necessary (step 1).
Write a Highlights section summarizing the most important features or changes in this release.
Copy the release notes and save them by clicking the grey Save draft button.
Open a new PR to update the version number in mesa/__init__.py and add the copied release notes to the HISTORY.md.
Once this PR is merged, return to the Releases section and publish the draft release.
The release.yml CI workflow should automatically create and upload the package to PyPI. Verify this on PyPI.org.
Finally, after release, open a new PR to update the version number in mesa/__init__.py for the next release (e.g., "3.1.0.dev").

A recorded video of this process is available here.

Special Thanks

A special thanks to the following projects who offered inspiration for this contributing file.

Django
18F's FOIA
18F's Midas

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