NiBabel Developer Guidelines

Also see Developer documentation page

NiBabel source code


Code Documentation

Please write documentation using Numpy documentation conventions:

Git Repository


The main release branch is called master. This is a merge-only branch. Features finished or updated by some developer are merged from the corresponding branch into master. At a certain point the current state of master is tagged – a release is done.

Only usable feature should end-up in master. Ideally master should be releasable at all times.

Additionally, there are distribution branches. They are prefixed dist/ and labeled after the packaging target (e.g. debian for a Debian package). If necessary, there can be multiple branches for each distribution target.


Official Debian packaging


Debian packaging of unofficial development snapshots. They do not go into the main Debian archive, but might be distributed through other channels (e.g. NeuroDebian).

Releases are merged into the packaging branches, packaging is updated if necessary and the branch gets tagged when a package version is released. Maintenance (as well as backport) releases or branches off from the respective packaging tag.

There might be additional branches for each developer, prefixed with initials. Alternatively, several GitHub (or elsewhere) clones might be used.


Please prefix all commit summaries with one (or more) of the following labels. This should help others to easily classify the commits into meaningful categories:

  • BF : bug fix

  • RF : refactoring

  • NF : new feature

  • BW : addresses backward-compatibility

  • OPT : optimization

  • BK : breaks something and/or tests fail

  • PL : making pylint happier

  • DOC: for all kinds of documentation related commits

  • TEST: for adding or changing tests


For easy tracking of what changes were absorbed during merge, we advise that you enable merge summaries within git:

git-config merge.summary true

See Configure git for more detail.


NiBabel uses tox to organize our testing and development workflows. tox runs tests in isolated environments that we specify, ensuring that we are able to test across many different environments, and those environments do not depend on our local configurations.

If you have the pipx tool installed, then you may simply:

pipx run tox

Alternatively, you can install tox and run it:

python -m pip install tox

This will run the tests in several configurations, with multiple sets of optional dependencies. If you have multiple versions of Python installed in your path, it will repeat the process for each version of Python iin our supported range. It may be useful to pick a particular version for rapid development:

tox -e py311-full-x64

This will run the environment using the Python 3.11 interpreter, with the full set of optional dependencies that are available for 64-bit interpreters. If you are using 32-bit Python, replace -x64 with -x86.

Style guide

To ensure code consistency and readability, NiBabel has adopted the following tools:

  • blue - An auto-formatter that aims to reduce diffs to relevant lines

  • isort_ - An import sorter that groups stdlib, third-party and local imports.

  • flake8 - A style checker that can catch (but generally not fix) common errors in code.

  • codespell - A spell checker targeted at source code.

  • pre-commit_ - A pre-commit hook manager that runs the above and various other checks/fixes.

While some amount of personal preference is involved in selecting and configuring auto-formatters, their value lies in largely eliminating the need to think or argue about style. With pre-commit turned on, you can write in the style that works for you, and the NiBabel style will be adopted prior to the commit.

To apply our style checks uniformly, simply run:

tox -e style,spellcheck

To fix any issues found:

tox -e style-fix
tox -e spellcheck -- -w

Occasionally, codespell has a false positive. To ignore the suggestion, add the intended word to tool.codespell.ignore-words-list in pyproject.toml. However, the ignore list is a blunt instrument and could cause a legitimate misspelling to be missed. Consider choosing a word that does not trigger codespell before adding it to the ignore list.

Pre-commit hooks

NiBabel uses pre-commit_ to help committers validate their changes before committing. To enable these, you can use pipx:

pipx run pre-commit install

Or install and run:

python -m pip install pre-commit
pre-commit install


The changelog is located in the toplevel directory of the source tree in the Changelog file. The content of this file should be formatted as restructured text to make it easy to put it into manual appendix and on the website.

This changelog should neither replicate the VCS commit log nor the distribution packaging changelogs (e.g. debian/changelog). It should be focused on the user perspective and is intended to list rather macroscopic and/or important changes to the module, like feature additions or bugfixes in the algorithms with implications to the performance or validity of results.

It may list references to 3rd party bugtrackers, in case the reported bugs match the criteria listed above.

Community guidelines

Please see our community guidelines. Other projects call these guidelines the “code of conduct”.