Contributing

Pull requests are more than welcome — both to the library and to the documentation. Some useful information:

We aim to follow PEP 8 in the library, but ignoring the 79-character-per-line limit, instead following a soft limit of 99, but allowing lines over this where it is the readable thing to do.
We aim to follow PEP 257 for all docstrings, and make them properly parseable by Sphinx while generating API documentation.
We keep pyflakes reporting no errors or warnings at all times.
We keep the master branch passing all tests at all times on all supported versions.

Travis CI is run against all pull requests and should enforce all of the above.

We use Opera Critic as an external code-review tool, which uses your GitHub login to authenticate. You'll get email notifications for issues raised in the review.

Patch submission guidelines

Create a new Git branch specific to your change. Do not put multiple fixes/features in the same pull request. If you find an unrelated bug, create a distinct branch and submit a separate pull request for the bugfix. This makes life much easier for maintainers and will speed up merging your patches.
Write a test whenever possible. Following existing tests is often easiest, and a good way to tell whether the feature you're modifying is easily testable.
Make sure documentation is updated. Keep docstrings current, and if necessary, update the Sphinx documentation in doc/.
Add a changelog entry at the top of CHANGES.rst following existing entries' styles.
Run tests with tox if possible, to make sure your changes are compatible with all supported Python versions.
Squash commits before submitting the pull request so that a single commit contains the entire change, and only that change (see the first bullet).
Don't rebase after creating the pull request. Merge with upstream, if necessary, and use git commit --fixup for fixing issues raised in a Critic review or by a failing Travis build. The reviewer will squash and rebase your pull request while accepting it. Even though GitHub won't recognize the pull request as accepted, the squashed commits will properly specify you as the author.
Attribute yourself in AUTHORS.rst.