Contributing to ASLPrep

ASLPrep is a project of the NiPreps Community, which provides detailed contributing guidelines. Please review the NiPreps contributing guidelines before contributing to ASLPrep.

This document picks up where the NiPreps contributing guidelines leave off. Specifically, it explains how to prepare a new development environment and update an existing environment, as necessary.

Development in Docker is encouraged, for the sake of consistency and portability. By default, work should be built off of pennlinc/aslprep:unstable, which tracks the main branch, or pennlinc/aslprep:latest, which tracks the latest release (see Installation for the basic procedure for running).

Contributing to ASLPrep without adding dependencies

In the most common case, you will want to modify ASLPrep’s Python code without adding any dependencies (Python or not) to the Docker image. In this situation, you can use the unstable Docker image without having to build a new Docker image yourself.

  1. Pull the unstable Docker image.

    docker pull pennlinc/aslprep:unstable
  2. Fork the ASLPrep repository to your GitHub account. For more information on contributing via the fork-and-branch approach, see GitHub’s contributing guide.

  3. Clone your forked repository to your local machine.

  4. Create a branch to work on. Make sure your branch is up to date with ASLPrep’s ``main`` branch before making any changes!

  5. Make changes to the codebase that you want to try out.

  6. Test our your changes by running the Docker container. The trick here is to mount your modified version of ASLPrep into the Docker container, overwriting the container’s version. This way, your Docker container will run using your modified code, rather than the original version.

    You can do this by running the Docker image as described in Usage Notes, but adding in a mount point for your code:

    docker run \
       -v /path/to/local/aslprep:/usr/local/miniconda/lib/python3.8/site-packages/aslprep \
       pennlinc/aslprep:unstable \
       ...  # see the usage documentation for info on what else to include in this command
  7. Push your changes to GitHub.

  8. Open a pull request to PennLINC/ASLPrep’s main branch. Please follow NiPreps contributing guidelines when preparing a pull request.

Running tests

While CircleCI will automatically run ASLPrep’s tests for any open PRs, we strongly recommend running at least some tests locally, to make sure your proposed changes work.

ASLPrep has a file, aslprep/tests/, that builds Docker run commands to run selected tests. Please use that script to run some tests locally before opening your PR.

Adding or modifying dependencies

If you think ASLPrep needs to use a library (Python or not) that is not installed in the Docker image already, then you will need to build a new Docker image to test out your proposed changes.

ASLPrep uses a “base Docker image” defined in We try to define the majority of non-Python requirements in that Docker image. If you want to add or modify a non-Python dependency, then you will need to clone that repository modify its Dockerfile, and build its Docker image to ensure that the new dependency installs correctly. Once that’s done, you can open a pull request to the aslprep_build repository with your change.


Given that this method requires contributing to two repositories, it’s a good idea to link to the associated ASLPrep issue in your aslprep_build PR.

For Python dependencies, you can update the requirements defined in ASLPrep’s pyproject.toml and rebuild the ASLPrep Docker image locally to test out your change. Once your change is working, you can open a pull request to the ASLPrep repo.