Today was the first day of EnHackathon: the Python open source contribution attempt of a couple of us working at Ensoft office, Cisco. Whilst it was a little overwhelming trying to find suitable points of contribution, especially in such a large and well-worn codebase, by the end of the day I had managed to make at least a dent into giving back to CPython.

TL;DR is in the Conclusions.

Starting Out

I started out by looking for issues on BPO, Python’s bug tracker which were marked with the newcomer-friendly keyword, as they are issues specifically marked out by maintainers as attainable first contributions.

I got a bit of luck, as almost all of the current newcomer-friendly issues had been chased up by fellow contributor Ben: he kindly let me take and work on a small task to add a new method to an existing implemented class in the unix_events module of asyncio. (bpo-38314)

The change basically requests that the method is_reading() is added to the read pipe transport for asyncio as implemented on UNIX systems, since it is available for other read transports described in the asyncio docs.

Making the Change

The change itself was fortunately quite simple: as you can see from the BPO comments, a maintainer and the issue raiser had basically suggested the implementation of the method: as a newcomer, I just had to familiarise myself with a bit of the internal state of the class.

Once I had made the change, I needed to add some tests: the best thing to do for this is to look under Lib/test for the overall module you’re contributing to and grep for the name of key methods or functions around those you’re adding to to find existing tests. The alternative if the tests are well laid out is to look for the file which tests the specific module you’re contributing to: for me, that was unix_events <=> test_unix_events (as is conventional).

Fortunately, the style of tests there was quite familiar to me (module unit tests making heavy use of unittest.mock), and had a preset structure I could copy, changing the assertions to constrain the functionality of my new method.

Raising the PR

Finally, the potentially scary part: raising the pull request so that my changes could be reviewed. As has been mentioned in other posts, there are some format requirements on PRs, but these are well-documented and not too onerous.

The trickier part is to get all of the necessary automation and bot interaction out of the way: one of the things that tripped me up was the creation of a NEWS.d entry to accompany my change: this will be marked in red by the news bot.

NEWS.d entries are needed for almost all Python changes, but especially in the case that it caused any outward change (like adding an API or change of behaviour): the exact need is documented on the devguide.

The process is a little confusing, but essentially:

  • Click on the Details tab of the bedevere/news bot checks item
  • Sign in to GitHub for blurb-it, and give it access to your <username>/cpython fork (or all repositories, if you really want)
  • Write your blurb and fill in the BPO and PR info: as suggested, don’t use the BPO number or PR number in the blurb as it appears in the NEWS.d entry filename
  • It generates a file and adds it to your PR, which should trigger the bedevere/news bot to re-check and mark the check as passed

By the end of the day, a maintainer had commented on the post to suggest some changes, and I’m currently working through resolving what the changes should be and making them. However, now that the PR is raised and all the hurdles from the CI are finished, I expect the rest of the fix to be the familiar coding and reviewing cycle(s).


  • Whilst the process of opening PRs can feel a bit daunting, it is quite rewarding once the PR exists and feels headed for merge.
  • Finding an issue can be tricky, but commenting on issues that seem to have stalled or looking for newcomer-friendly tags are good ways to get started. Even just causing an issue to be closed or reopening the dialogue on a change are good contributions to such a large machine!
  • There are some hurdles to raising the PR and getting it ready for merge, but these are largely well documented on the devguide.
  • There’s definitely still items out there which the CPython community could use help with, despite the codebase’s size and age, so there’s still a lot of reward to be had in contributing!