Maintaining and Developing

This will be a guide in how to contribute to Simphony by writing code. We will go over how to set up a development environment, testing, how to make a pull request, and how to release a version of Simphony. This guide assumes you have a good understanding of Python development and Git.

Setting Up the Environment

Simphony is a Python 3 package, and so we recommend using the built-in venv module for Python 3 to create a virtual environment. From this point forwards, all commands that we provide assume that your new virtual environment is activated.

After creating and activating your virtual environment, go to the Simphony Github page and fork the project. You should now have your own copy of the repository on Github. Run:

git clone[your username]/simphony.git

to download the Github repository onto your machine. You will also want to run:

git remote add upstream

This will allow you to pull any changes made to the original repository.

Once those steps are complete, run the command:

make install

in the root directory of Simphony. This will build the development version of Simphony as a package in your virtual environment. The build will update whenever you update Simphony code on your machine, allowing you to use/import the development version in Python files.

You can now start writing your changes to Simphony code. Make sure to always pull changes from upstream before starting development.


We expect code to be thoroughly tested before it gets merged with the main Simphony repository.

In Simphony, we include a tests directory inside main sections of code, where we write tests using the pytest framework. You should write new tests in these test directories for any new code you develop.

Your code should pass all existing tests before submitting a pull request. Any time you make a commit, a pre-commit hook will run some basic tests and formatters. To run all tests, run the command:

make test

in the root directory of Simphony. You may also wish to run an individual test, by using:

pytest path_to_test/

Specific formatting issues must also be checked before changes will be merged. You can check all formatting issues using:


An additional step you can take with your tests is to measure the test coverage of your code. To do this, install pytest-cov, then run the command:

pytest --cov=simphony tests/

A final check you may perform before submitting any pull requests is to ensure that your Simphony package will install properly. This is mainly necessary if you intend to release a new version of Simphony. To test this, remove all current installations of Simphony (repeat the command pip uninstall simphony until no versions remain) and then run the following commands from Simphony’s root directory:

python3 sdist bdist_wheel
pip3 install dist/simphony-[VERSION].tar.gz


Doing this will require you to rebuild your development version of Simphony using make install again. Before you do this, remove the test version of Simphony you just installed using pip uninstall simphony once more.

Make a Pull Request

After you’ve made your changes and have done the testing steps above, you’re ready to make a pull request. Push your changes to your Github fork, and navigate to the fork’s page on Github. You should see a button that will create a pull request for you.

Reviewers will look over your pull request before merging your changes into the main repository, so we expect you to write a clear and concise explanation of your changes attached to your pull request. If your changes are extensive, you will likely need to write more explanation, and perhaps explain the motivation for such extensive changes. Your description of the changes you’ve made will be used when writing the release notes.

Reviewers will comment on any last minute changes they want to see before merging, such as style and inline documentation, so make sure your code is polished before submitting a pull request. All documentation should follow the numpy doc formatting standard.


If you need to make changes while a pull request is still being reviewed, just push your changes to your fork. The pull request will automatically update to match.

When you submit a pull request, automatic tests will trigger and run through Github’s services. These must all pass before your pull request will be accepted. If any fail, click the red cross to pull up a test log, which will help you find out why they failed. Ideally, you will have tested your project before creating the pull request in the first place, so that these tests will not fail.

Finally, when the reviewers believe that the pull request is ready, they will approve the pull request and it will be merged into the main repository.


Most contributors won’t have to worry about the release process, since this is up to the core development team. It may still be informative, so we include it here.

The release process is handled by GitHub Actions. When the release script is triggered, it builds the package for Python 3.6-3.8 for Windows, Mac and Linux. It uploads the package to PyPI, creates a GitHub release, and updates the documentation to the most recent stable release.

Before the release, all deprecated code should be removed, and a changelog should be written for the new version. For the changelog, follow the style of previous changelogs when writing. The documentation should be ready for build, see Documenting for how to build. Use bump2version to update the version number throughout the project.

Once all of this is complete, run the bash script at scripts/release, and the rest will be taken care of automatically.