How To Contribute

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

This document is mainly to help you to get started by codifying tribal knowledge and expectations and make it more accessible to everyone. But don’t be afraid to open half-finished PRs and ask questions if something is unclear!

Workflow

  • 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.

  • Since we squash on merge, it’s up to you how you handle updates to the main branch. Whether you prefer to rebase on main or merge main into your branch, do whatever is more comfortable for you.

  • Always add tests and docs for your code. This is a hard rule; patches with missing tests or documentation can’t be merged.

  • Consider updating CHANGELOG.rst to reflect the changes as observed by people using this library.

  • 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, so we know you’re done.

  • Don’t break backward compatibility.

Code

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

    def func(x):
        """
        Do 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:: 17.1.0 WHAT.

  • We use isort to sort our imports, and we follow the Black code style with a line length of 79 characters. As long as you run our full tox suite before committing, or install our pre-commit hooks (ideally you’ll do both – see below “Local Development Environment”), you won’t have to spend any time on formatting your code at all. If you don’t, CI will catch it for you – but that seems like a waste of your time!

Tests

  • Write your asserts as expected == actual to line them up nicely and leave an empty line before them:

    .. code-block:: python
    

    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 in our CI. If you lack some Python versions, you can can make it a non-failure using tox --skip-missing-interpreters (in that case you may want to look into asdf or pyenv that make it very easy to install many different Python versions in parallel).

  • Write good test docstrings.

Documentation

  • 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 except if two headers follow immediately after each other:

    Last line of previous section.
    
    
    Header of New Top Section
    -------------------------
    
    Header of New Section
    ^^^^^^^^^^^^^^^^^^^^^
    
    First line of new section.
    
  • If your change is noteworthy, add an entry to the changelog. Use semantic newlines, and add a link to your pull request:

    - Added ``pem.func()`` that does foo.
      It's pretty cool.
      `#1 <https://github.com/hynek/pem/pull/1>`_
    - ``pem.func()`` now doesn't crash the Large Hadron Collider anymore.
      That was a nasty bug!
      `#2 <https://github.com/hynek/pem/pull/2>`_
    

Local Development Environment

You can (and should) run our test suite using tox. However, you’ll probably want a more traditional environment as well. We highly recommend to develop using the latest Python 3 release because you’re more likely to catch certain bugs earlier.

First create a virtual environment. It’s out of scope for this document to list all the ways to manage virtual environments in Python, but if you don’t already have a pet way, take some time to look at tools like pew, virtualfish, virtualenvwrapper, and direnv’s Python support.

Next get an up to date checkout of the pem repository:

git clone git@github.com:hynek/pem.git

Change into the newly created directory and after activating your virtual environment install an editable version of pem along with its tests and docs requirements:

cd pem
pip install -e .[dev]

At this point,

$ python -m pytest

should work and pass, as should:

$ cd docs
$ make html

The built documentation can then be found in docs/_build/html/.

To avoid committing code that violates our style guide, we strongly advice you to install pre-commit 1 hooks:

$ pre-commit install

You can also run them anytime (as our tox does) using:

$ pre-commit run --all-files
1

pre-commit should have been installed into your virtualenv automatically when you ran pip install -e .[dev] above. If pre-commit is missing, it may be that you need to re-run pip install -e .[dev].


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 pem!