Contributing to Mypy

Welcome! Mypy is a community project that aims to work for a wide range of Python users and Python codebases. If you're trying Mypy on your Python code, your experience and what you can contribute are important to the project's success.

Getting started, building, and testing

If you haven't already, take a look at the project's README.md file and the Mypy documentation, and try adding type annotations to your file and type-checking it with Mypy.

Discussion

If you've run into behavior in Mypy you don't understand, or you're having trouble working out a good way to apply it to your code, or you've found a bug or would like a feature it doesn't have, we want to hear from you!

Our main forum for discussion is the project's GitHub issue tracker. This is the right place to start a discussion of any of the above or most any other topic concerning the project.

We have an IRC channel, #python-mypy on irc.freenode.net. This is lightly used, but some Mypy core developers are almost always present; feel free to find us there and we're happy to chat. Substantive technical discussion will be directed to the issue tracker.

Code of Conduct

Everyone participating in the Mypy community, and in particular in our issue tracker, pull requests, and IRC channel, is expected to treat other people with respect and more generally to follow the guidelines articulated in the Python Community Code of Conduct.

Submitting Changes

Even more excellent than a good bug report is a fix for a bug, or the implementation of a much-needed new feature. (*) We'd love to have your contributions.

(*) If your new feature will be a lot of work, we recommend talking to us early -- see below.

We use the usual GitHub pull-request flow, which may be familiar to you if you've contributed to other projects on GitHub. For the mechanics, see our git and GitHub workflow help page, or GitHub's own documentation.

Anyone interested in Mypy may review your code. One of the Mypy core developers will merge your pull request when they think it's ready. For every pull request, we aim to promptly either merge it or say why it's not yet ready; if you go a few days without a reply, please feel free to ping the thread by adding a new comment.

At present the core developers are (alphabetically): David Fisher (@ddfisher) Jukka Lehtosalo (@JukkaL) Greg Price (@gnprice) Guido van Rossum (@gvanrossum)

Preparing Changes

Before you begin: if your change will be a significant amount of work to write, we highly recommend starting by opening an issue laying out what you want to do. That lets a conversation happen early in case other contributors disagree with what you'd like to do or have ideas that will help you do it.

The best pull requests are focused, clearly describe what they're for and why they're correct, and contain tests for whatever changes they make to the code's behavior. As a bonus these are easiest for someone to review, which helps your pull request get merged quickly! Standard advice about good pull requests for open-source projects applies; we have our own writeup of this advice.

See also our coding conventions -- which consist mainly of a reference to PEP 8 -- for the code you put in the pull request.

You may also find other pages in the Mypy developer guide helpful in developing your change.

Issue-tracker conventions

We aim to reply to all new issues promptly. We'll assign a milestone to help us track which issues we intend to get to when, and may apply labels to carry some other information. Here's what our milestones and labels mean.

Milestones

We use GitHub "milestones" (see our list) to roughly order what we want to do soon and less soon.

This means they represent a combination of priority and scale of work. Bugs that aren't a huge deal but do matter to users and don't seem like a lot of work to fix generally go in a near milestone; things that will take longer may go further out.

Specifically:

• Numbered milestones correspond to releases. These assignments are changeable, and issues may be moved earlier or later. Assignments to further-out milestones are more likely to change.
• Point releases, like 0.x.y when we're already at 0.x.z, generally have issues that are less work to tackle and whose user-facing impact is small or a bugfix. Meatier or more radical issues generally go to a full "minor" release, like 0.x.0.
• Future has other things we don't currently plan to get to anytime soon -- akin to "backlog" in some systems.
• Questions is for issue threads where a user is asking a question but it isn't yet clear that it represents something to actually change. We use the issue tracker as the preferred venue for such questions, even when they aren't literally issues, to keep down the number of distinct discussion venues anyone needs to track. These might move to a different milestone if after discussion a bug or feature request emerges.
• Issues without a milestone haven't been triaged. We aim to triage all new issues promptly, but there are some issues from 2015 and earlier that we haven't yet reviewed for triage since adopting these conventions.

Labels

• needs discussion: This issue needs agreement on some kind of design before it makes sense to implement it, and it either doesn't yet have a design or doesn't yet have agreement on one.
• feature, bug, refactoring: These classify the user-facing impact of the change. Specifically "refactoring" means there should be no user-facing effect.
• duplicate, wontfix: These identify issues that we've closed for the respective reasons.
• priority, question, postponed: These labels predate the milestone conventions and are deprecated; they should be gone on all issues that have been triaged to a milestone.