# NiBabel

### Access a cacophony of neuro-imaging file formats

# Core Developer Guide

As a core developer, you should continue making pull requests in accordance with the NiBabel Developer Guidelines. You are responsible for shepherding other contributors through the review process. You also have the ability to merge or approve other contributors’ pull requests.

## Reviewing

### How to Conduct A Good Review

Always be kind to contributors. Nearly all of Nibabel is volunteer work, for which we are tremendously grateful. Provide constructive criticism on ideas and implementations, and remind yourself of how it felt when your own work was being evaluated as a novice.

Nibabel strongly values mentorship in code review. New users often need more handholding, having little to no git experience. Repeat yourself liberally, and, if you don’t recognize a contributor, point them to our development guide, or other GitHub workflow tutorials around the web. Do not assume that they know how GitHub works (e.g., many don’t realize that adding a commit automatically updates a pull request). Gentle, polite, kind encouragement can make the difference between a new core developer and an abandoned pull request.

When reviewing, focus on the following:

1. API: The API is what users see when they first use Nibabel. APIs are difficult to change once released, so should be simple, consistent with other parts of the library, and should avoid side-effects such as changing global state or modifying input variables.

2. Documentation: Any new feature should have a tutorial example that not only illustrates but explains it.

3. The algorithm: You should understand the code being modified or added before approving it. (See Merge Only Changes You Understand below.) Implementations should do what they claim, and be simple, readable, and efficient.

4. Tests: All contributions to the library must be tested, and each added line of code should be covered by at least one test. Good tests not only execute the code, but explore corner cases. It is tempting not to review tests, but please do so.

Other changes may be nitpicky: spelling mistakes, formatting, etc. Do not ask contributors to make these changes, and instead make the changes by pushing to their branch, or using GitHub’s suggestion feature. (The latter is preferred because it gives the contributor a choice in whether to accept the changes.)

Please add a note to a pull request after you push new changes; GitHub may not send out notifications for these.

### Merge Only Changes You Understand

Long-term maintainability is an important concern. Code doesn’t merely have to work, but should be understood by multiple core developers. Changes will have to be made in the future, and the original contributor may have moved on.

Therefore, do not merge a code change unless you understand it. Ask for help freely: we have a long history of consulting community members, or even external developers, for added insight where needed, and see this as a great learning opportunity.

While we collectively “own” any patches (and bugs!) that become part of the code base, you are vouching for changes you merge. Please take that responsibility seriously.

## Closing issues and pull requests

Sometimes, an issue must be closed that was not fully resolved. This can be for a number of reasons:

- the person behind the original post has not responded to calls for clarification, and none of the core developers have been able to reproduce their issue;

- fixing the issue is difficult, and it is deemed too niche a use case to devote sustained effort or prioritize over other issues; or

- the use case or feature request is something that core developers feel does not belong in Nibabel,

among others. Similarly, pull requests sometimes need to be closed without merging, because:

- the pull request implements a niche feature that we consider not worth the added maintenance burden;

- the pull request implements a useful feature, but requires significant effort to bring up to Nibabel’s standards, and the original contributor has moved on, and no other developer can be found to make the necessary changes; or

- the pull request makes changes that make maintenance harder, such as increasing the code complexity of a function significantly to implement a marginal speedup,

among others.

All these may be valid reasons for closing, but we must be wary not to alienate contributors by closing an issue or pull request without an explanation. When closing, your message should:

- explain clearly how the decision was made to close. This is particularly important when the decision was made in a community meeting, which does not have as visible a record as the comments thread on the issue itself;

- thank the contributor(s) for their work; and

- provide a clear path for the contributor or anyone else to appeal the decision.

These points help ensure that all contributors feel welcome and empowered to keep contributing, regardless of the outcome of past contributions.

## Further resources

As a core member, you should be familiar with community and developer resources such as:

- Our NiBabel Developer Guidelines

- Our Community guidelines

- PEP8 for Python style

- PEP257 and the NumPy documentation guide for docstrings. (NumPy docstrings are a superset of PEP257. You should read both.)

- The Nibabel tag on NeuroStars

- Our mailing list

Please do monitor any of the resources above that you find helpful.

# Acknowledgments

This document is based on the NetworkX Core Developer guide.