Skip to content

Instantly share code, notes, and snippets.

What would you like to do?
Initial email about Python development process and proposed improvements

This was posted as an email to python-dev.

History lesson

Since I signed up for the python-dev mailing list way back in June 2002, there seems to be a cycle where we as a group come to a realization that our current software development process has not kept up with modern practices and could stand for an update. For me this was first shown when we moved from SourceForge to our own infrastructure, then again when we moved from Subversion to Mercurial (I led both of these initiatives, so it's somewhat a tradition/curse I find myself in this position yet again). And so we again find ourselves at the point of realizing that we are not keeping up with current practices and thus need to evaluate how we can improve our situation.

Where we are now

Now it should be realized that we have to sets of users of our development process: contributors and core developers (the latter whom can play both roles). If you take a rough outline of our current, recommended process it goes something like this:

  1. Contributor clones a repository from
  2. Contributor makes desired changes
  3. Contributor generates a patch
  4. Contributor creates account on and signs the contributor agreement
  5. Contributor creates an issue on (if one does not already exist) and uploads a patch
  6. Core developer evaluates patch, possibly leaving comments through our custom version of Rietveld
  7. Contributor revises patch based on feedback and uploads new patch
  8. Core developer downloads patch and applies it to a clean clone
  9. Core developer runs the tests
  10. Core developer does one last hg pull -u and then commits the changes to various branches

I think we can all agree it works to some extent, but isn't exactly smooth. There are multiple steps in there -- in full or partially -- that can be automated. There is room to improve everyone's lives.

And we can't forget the people who help keep all of this running as well. There are those that manage the SSH keys, the issue tracker, the review tool,, and the email system that let's use know when stuff happens on any of these other systems. The impact on them needs to also be considered.


I see two scenarios for contributors to optimize for. There's the simple spelling mistake patches and then there's the code change patches. The former is the kind of thing that you can do in a browser without much effort and should be a no-brainer commit/reject decision for a core developer. This is what the GitHub/Bitbucket camps have been promoting their solution for solving while leaving the cpython repo alone. Unfortunately the bulk of our documentation is in the Doc/ directory of cpython. While it's nice to think about moving the devguide, peps, and even breaking out the tutorial to repos hosting on Bitbucket/GitHub, everything else is in Doc/ (language reference, howtos, stdlib, C API, etc.). So unless we want to completely break all of Doc/ out of the cpython repo and have core developers willing to edit two separate repos when making changes that impact code and docs, moving only a subset of docs feels like a band-aid solution that ignores the big, white elephant in the room: the cpython repo, where a bulk of patches are targeting.

For the code change patches, contributors need an easy way to get a hold of the code and get their changes to the core developers. After that it's things like letting contributors knowing that their patch doesn't apply cleanly, doesn't pass tests, etc. As of right now getting the patch into the issue tracker is a bit manual but nothing crazy. The real issue in this scenario is core developer response time.

Core developers

There is a finite amount of time that core developers get to contribute to Python and it fluctuates greatly. This means that if a process can be found which allows core developers to spend less time doing mechanical work and more time doing things that can't be automated -- namely code reviews -- then the throughput of patches being accepted/rejected will increase. This also impacts any increased patch submission rate that comes from improving the situation for contributors because if the throughput doesn't change then there will simply be more patches sitting in the issue tracker and that doesn't benefit anyone.

My ideal scenario

If I had an infinite amount of resources (money, volunteers, time, etc.), this would be my ideal scenario:

  1. Contributor gets code from wherever; easiest to just say "fork on GitHub or Bitbucket" as they would be official mirrors of and are updated after every commit, but could clone if they wanted
  2. Contributor makes edits; if they cloned on Bitbucket or GitHub then they have browser edit access already
  3. Contributor creates an account at and signs the CLA
  4. The contributor creates an issue at (probably the one piece of infrastructure we all agree is better than the other options, although its workflow could use an update)
  5. If the contributor used Bitbucket or GitHub, they send a pull request with the issue # in the PR message
  6. notices the PR, grabs a patch for it, and puts it on for code review
  7. CI runs on the patch based on what Python versions are specified in the issue tracker, letting everyone know if it applied cleanly, passed tests on the OSs that would be affected, and also got a test coverage report
  8. Core developer does a code review
  9. Contributor updates their code based on the code review and the updated patch gets pulled by automatically and CI runs again
  10. Once the patch is acceptable and assuming the patch applies cleanly to all versions to commit to, the core developer clicks a "Commit" button, fills in a commit message and NEWS entry, and everything gets committed (if the patch can't apply cleanly then the core developer does it the old-fashion way, or maybe auto-generate a new PR which can be manually touched up so it does apply cleanly?)

Basically the ideal scenario lets contributors use whatever tools and platforms that they want and provides as much automated support as possible to make sure their code is tip-top before and during code review while core developers can review and commit patches so easily that they can do their job from a beach with a tablet and some WiFi.

Where the current proposed solutions seem to fall short


Basically GitHub/Bitbucket is a win for contributors but doesn't buy core developers that much. GitHub/Bitbucket gives contributors the easy cloning, drive-by patches, CI, and PRs. Core developers get a code review tool -- I'm counting Rietveld as deprecated after Guido's comments about the code's maintenance issues -- and push-button commits only for single branch changes. But for any patch that crosses branches we don't really gain anything. At best core developers tell a contributor "please send your PR against 3.4", push-button merge it, update a local clone, merge from 3.4 to default, do the usual stuff, commit, and then push; that still keeps me off the beach, though, so that doesn't get us the whole way. You could force people to submit two PRs, but I don't see that flying. Maybe some tool could be written that automatically handles the merge/commit across branches once the initial PR is in? Or automatically create a PR that core developers can touch up as necessary and then accept that as well? Regardless, some solution is necessary to handle branch-crossing PRs.

As for GitHub vs. Bitbucket, I personally don't care. I like GitHub's interface more, but that's personal taste. I like hg more than git, but that's also personal taste (and I consider a transition from hg to git a hassle but not a deal-breaker but also not a win). It is unfortunate, though, that under this scenario we would have to choose only one platform.

It's also unfortunate both are closed-source, but that's not a deal-breaker, just a knock against if the decision is close.

Our own infrastructure

The shortcoming here is the need for developers, developers, developers! Everything outlined in the ideal scenario is totally doable on our own infrastructure with enough code and time (donated/paid-for infrastructure shouldn't be an issue). But historically that code and time has not materialized. Our code review tool is a fork that probably should be replaced as only Martin von Löwis can maintain it. Basically Ezio Melotti maintains the issue tracker's code. We don't exactly have a ton of people constantly going "I'm so bored because everything for Python's development infrastructure gets sorted so quickly!" A perfect example is that R. David Murray came up with a nice update for our workflow after PyCon but then ran out of time after mostly defining it and nothing ever became of it (maybe we can rectify that at PyCon?). Eric Snow has pointed out how he has written similar code for pulling PRs from I think GitHub to another code review tool, but that doesn't magically make it work in our infrastructure or get someone to write it and help maintain it (no offense, Eric).

IOW our infrastructure can do anything, but it can't run on hopes and dreams. Commitments from many people to making this happen by a certain deadline will be needed so as to not allow it to drag on forever. People would also have to commit to continued maintenance to make this viable long-term.

Next steps

I'm thinking first draft PEPs by February 1 to know who's all-in (8 weeks away), all details worked out in final PEPs and whatever is required to prove to me it will work by the PyCon language summit (4 months away). I make a decision by May 1, and then implementation aims to be done by the time 3.5.0 is cut so we can switch over shortly thereafter (9 months away). Sound like a reasonable timeline?


This comment has been minimized.

Copy link

@dstufft dstufft commented Dec 5, 2014

One comment: Bitbucket supports both Mercurial and git, so it's not entirely unreasonable to host a project on both sites.


This comment has been minimized.

Copy link

@dstufft dstufft commented Dec 5, 2014

Also note: You can create a PR from one branch to another completely within the Github UI. This works pretty well if the original PR was made against the "stable" branch and not the "development" branch to allow you to merge a patch into another without having to hit the command line.


This comment has been minimized.

Copy link

@willingc willingc commented Dec 6, 2014

@brettcannon Happy to help. Since most involved in the discussion are core developers, I would like to comment from a "contributor" standpoint.

Since increasing developers is a goal above, helping new "contributors" make a successful "commit" in a timely fashion is critical to contributors continuing to donate their development time ongoing to a project.

Between steps 1 and 2 in your current state and the ideal solution, there is a crucial step for "contributors" -- finding a suitable issues to work on. Step 1.5 could be "present contributors a way to find suitable issues" i.e. curating issues for newcomers, better documentation, more triaging of issues for clarity, labeling stale issues, etc. I think curation of issues and a focused effort on building the contributor pipeline is important.

FWIW, it would be good to move away from language like "simple" spelling patches vs code change patches. I know what you are trying to say, but "simple" patches really would be more encouraging and welcoming as "straightforward and bitesize" patches. Getting that first commit in is as more about understanding the project workflow than the complexity of the patch. IMHO, bravo on moving this forward 🍰


This comment has been minimized.

Copy link

@vsajip vsajip commented Dec 7, 2014

Another drawback of the Github/BitBucket route (vs. own infrastructure) is that there very limited scope to customise to future requirements (even if they meet current requirements). I know lack of developer availability means that there may be less of a difference in practice, but at least in principle customisation would be possible where the infrastructure is under control.


This comment has been minimized.

Copy link

@westurner westurner commented Dec 9, 2014

What a script! Can it just permute until the tests pass?

This is really succint. IIUC, this spans many of the documents linked to by the "Contributing" section of the devguide:

Sign up for free to join this conversation on GitHub. Already have an account? Sign in to comment