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How To Contribute

First off, thank you for considering contributing to attrs! It's people like you who make it is such a great tool for everyone.

Here are a few guidelines to get you started (but don't be afraid to open half-finished PRs and ask questions if something is unclear!):


  • No contribution is too small! Please submit as many fixes for typos and grammar bloopers as you can!
  • Try to limit each pull request to one change only.
  • Always add tests and docs for your code. This is a hard rule; patches with missing tests or documentation can't be accepted.
  • Make sure your changes pass our CI. You won't get any feedback until it's green unless you ask for it.
  • Once you've addressed review feedback, make sure to bump the pull request with a short note. Maintainers don’t receive notifications when you push new commits.
  • Don’t break backward compatibility.


  • Obey PEP 8 and PEP 257. We use the """-on-separate-lines style for docstrings:

    def func(x):
        Does something.
        :param str x: A very important parameter.
        :rtype: str
  • If you add or change public APIs, tag the docstring using .. versionadded:: 16.0.0 WHAT or .. versionchanged:: 16.2.0 WHAT.

  • Prefer double quotes (") over single quotes (') unless the string contains double quotes itself.


  • Write your asserts as expected == actual to line them up nicely:

    x = f()
    assert 42 == x.some_attribute
    assert "foo" == x._a_private_attribute
  • To run the test suite, all you need is a recent tox. It will ensure the test suite runs with all dependencies against all Python versions just as it will on Travis CI. If you lack some Python versions, you can can always limit the environments like tox -e py27,py35 (in that case you may want to look into pyenv, which makes it very easy to install many different Python versions in parallel).

  • Write good test docstrings.

  • To ensure new features work well with the rest of the system, they should be also added to our Hypothesis testing strategy which you find in tests/


  • Use semantic newlines in reStructuredText files (files ending in .rst):

    This is a sentence.
    This is another sentence.
  • If you start a new section, add two blank lines before and one blank line after the header:

    Last line of previous section.
    Header of New Section
    First line of new section.
  • If you add a new feature, demonstrate its awesomeness in the examples page!

  • If your change is noteworthy, add an entry to the changelog. Use present tense, semantic newlines, and add a link to your pull request:

    - Add awesome new feature.
      The feature really *is* awesome.
      [`#1 <>`_]
    - Fix nasty bug.
      The bug really *was* nasty.
      [`#2 <>`_]

Again, this list is mainly to help you to get started by codifying tribal knowledge and expectations. If something is unclear, feel free to ask for help!

Please note that this project is released with a Contributor Code of Conduct. By participating in this project you agree to abide by its terms. Please report any harm to Hynek Schlawack in any way you find appropriate.

Thank you for considering contributing to attrs!