Development workflow#

Workflow summary#

To keep your work well organized, with readable history, and in turn make it easier for project maintainers (that might be you) to see what you've done, and why you did it, we recommend the following:

  • Don't make changes in your local main branch!

  • Before starting a new set of changes, fetch all changes from upstream/main, and start a new feature branch from that.

  • Make a new branch for each feature or bug fix — "one task, one branch".

  • Name your branch for the purpose of the changes - e.g. bugfix-for-issue-14 or refactor-database-code.

  • If you get stuck, reach out on Gitter or discourse.

  • When you're ready or need feedback on your code, open a pull request so that the Matplotlib developers can give feedback and eventually include your suggested code into the main branch.

Update the main branch#

First make sure you have followed Setting up Matplotlib for development.

From time to time you should fetch the upstream changes from GitHub:

git fetch upstream

This will pull down any commits you don't have, and set the remote branches to point to the right commit.

Make a new feature branch#

When you are ready to make some changes to the code, you should start a new branch. Branches that are for a collection of related edits are often called 'feature branches'.

Making a new branch for each set of related changes will make it easier for someone reviewing your branch to see what you are doing.

Choose an informative name for the branch to remind yourself and the rest of us what the changes in the branch are for. For example add-ability-to-fly, or bugfix-for-issue-42.

# Update the main branch
git fetch upstream
# Make new feature branch starting at current main
git branch my-new-feature upstream/main
git checkout my-new-feature

If you started making changes on your local main branch, you can convert the branch to a feature branch by renaming it:

git branch -m <newname>

Generally, you will want to keep your feature branches on your public GitHub fork of Matplotlib. To do this, you git push this new branch up to your GitHub repo. Generally, if you followed the instructions in these pages, and by default, git will have a link to your fork of the GitHub repo, called origin. You push up to your own fork with:

git push origin my-new-feature

In git >= 1.7 you can ensure that the link is correctly set by using the --set-upstream option:

git push --set-upstream origin my-new-feature

From now on git will know that my-new-feature is related to the my-new-feature branch in the GitHub repo.

If you first opened the pull request from your main branch and then converted it to a feature branch, you will need to close the original pull request and open a new pull request from the renamed branch. See GitHub: working with branches.

The editing workflow#

  1. Make some changes

  2. Save the changes

  3. See which files have changed with git status. You'll see a listing like this one:

    # On branch ny-new-feature
# Changed but not updated:
#   (use "git add <file>..." to update what will be committed)
#   (use "git checkout -- <file>..." to discard changes in working directory)
#
#  modified:   README
#
# Untracked files:
#   (use "git add <file>..." to include in what will be committed)
#
#  INSTALL
no changes added to commit (use "git add" and/or "git commit -a")

  4. Check what the actual changes are with git diff.

  5. Add any new files to version control git add new_file_name.

  6. To commit all modified files into the local copy of your repo, type:

    git commit -am 'A commit message'

    Note the -am options to commit. The m flag signals that you are going to type a message on the command line. The a flag stages every file that has been modified, except files listed in .gitignore. For more information, see why the -a flag? and the git commit manual page.

  7. To push the changes up to your forked repo on GitHub, do a git push.

Open a pull request#

When you are ready to ask for someone to review your code and consider a merge, submit your Pull Request (PR).

Enter a title for the set of changes with some explanation of what you've done. Mention anything you'd like particular attention for - such as a complicated change or some code you are not happy with.

If you don't think your request is ready to be merged, just say so in your pull request message and use the "Draft PR" feature of GitHub. This is a good way of getting some preliminary code review.

Update a pull request#

When updating your pull request after making revisions, instead of adding new commits, please consider amending your initial commit(s) to keep the commit history clean.

You can achieve this by using

git commit -a --amend --no-edit
git push [your-remote-repo] [your-branch] --force-with-lease

Manage commit history#

Explore your repository#

To see a graphical representation of the repository branches and commits:

gitk --all

To see a linear list of commits for this branch:

git log

Recover from mistakes#

Sometimes, you mess up merges or rebases. Luckily, in git it is relatively straightforward to recover from such mistakes.

If you mess up during a rebase:

git rebase --abort

If you notice you messed up after the rebase:

# reset branch back to the saved point
git reset --hard tmp

If you forgot to make a backup branch:

# look at the reflog of the branch
git reflog show cool-feature

8630830 cool-feature@{0}: commit: BUG: io: close file handles immediately
278dd2a cool-feature@{1}: rebase finished: refs/heads/my-feature-branch onto 11ee694744f2552d
26aa21a cool-feature@{2}: commit: BUG: lib: make seek_gzip_factory not leak gzip obj
...

# reset the branch to where it was before the botched rebase
git reset --hard cool-feature@{2}

Rewrite commit history#

Note

Do this only for your own feature branches.

Is there an embarrassing typo in a commit you made? Or perhaps you made several false starts you don't want posterity to see.

This can be done via interactive rebasing.

Suppose that the commit history looks like this:

git log --oneline
eadc391 Fix some remaining bugs
a815645 Modify it so that it works
2dec1ac Fix a few bugs + disable
13d7934 First implementation
6ad92e5 * masked is now an instance of a new object, MaskedConstant
29001ed Add pre-nep for a copule of structured_array_extensions.
...

and 6ad92e5 is the last commit in the cool-feature branch. Suppose we want to make the following changes:

  • Rewrite the commit message for 13d7934 to something more sensible.

  • Combine the commits 2dec1ac, a815645, eadc391 into a single one.

We do as follows:

# make a backup of the current state
git branch tmp HEAD
# interactive rebase
git rebase -i 6ad92e5

This will open an editor with the following text in it:

pick 13d7934 First implementation
pick 2dec1ac Fix a few bugs + disable
pick a815645 Modify it so that it works
pick eadc391 Fix some remaining bugs

# Rebase 6ad92e5..eadc391 onto 6ad92e5
#
# Commands:
#  p, pick = use commit
#  r, reword = use commit, but edit the commit message
#  e, edit = use commit, but stop for amending
#  s, squash = use commit, but meld into previous commit
#  f, fixup = like "squash", but discard this commit's log message
#
# If you remove a line here THAT COMMIT WILL BE LOST.
# However, if you remove everything, the rebase will be aborted.
#

To achieve what we want, we will make the following changes to it:

r 13d7934 First implementation
pick 2dec1ac Fix a few bugs + disable
f a815645 Modify it so that it works
f eadc391 Fix some remaining bugs

This means that (i) we want to edit the commit message for 13d7934, and (ii) collapse the last three commits into one. Now we save and quit the editor.

Git will then immediately bring up an editor for editing the commit message. After revising it, we get the output:

[detached HEAD 721fc64] FOO: First implementation
 2 files changed, 199 insertions(+), 66 deletions(-)
[detached HEAD 0f22701] Fix a few bugs + disable
 1 files changed, 79 insertions(+), 61 deletions(-)
Successfully rebased and updated refs/heads/my-feature-branch.

and now, the history looks like this:

0f22701 Fix a few bugs + disable
721fc64 ENH: Sophisticated feature
6ad92e5 * masked is now an instance of a new object, MaskedConstant

If it went wrong, recovery is again possible as explained above.

If you have not yet pushed this branch to github, you can carry on as normal, however if you have already pushed this commit see Push with force for how to replace your already published commits with the new ones.

Rebase onto upstream/main#

Let's say you thought of some work you'd like to do. You Update the main branch and Make a new feature branch called cool-feature. At this stage, main is at some commit, let's call it E. Now you make some new commits on your cool-feature branch, let's call them A, B, C. Maybe your changes take a while, or you come back to them after a while. In the meantime, main has progressed from commit E to commit (say) G:

      A---B---C cool-feature
     /
D---E---F---G main

At this stage you consider merging main into your feature branch, and you remember that this page sternly advises you not to do that, because the history will get messy. Most of the time, you can just ask for a review without worrying about whether main has got a little ahead; however sometimes, the changes in main might affect your changes, and you need to harmonize them. In this situation you may prefer to do a rebase.

rebase takes your changes (A, B, C) and replays them as if they had been made to the current state of main. In other words, in this case, it takes the changes represented by A, B, C and replays them on top of G. After the rebase, your history will look like this:

              A'--B'--C' cool-feature
             /
D---E---F---G main

See rebase without tears for more detail.

To do a rebase on upstream/main:

# Fetch changes from upstream/main
git fetch upstream
# go to the feature branch
git checkout cool-feature
# make a backup in case you mess up
git branch tmp cool-feature
# rebase cool-feature onto main
git rebase --onto upstream/main upstream/main cool-feature

In this situation, where you are already on branch cool-feature, the last command can be written more succinctly as:

git rebase upstream/main

When all looks good, you can delete your backup branch:

git branch -D tmp

If it doesn't look good you may need to have a look at Recover from mistakes.

If you have made changes to files that have also changed in main, this may generate merge conflicts that you need to resolve - see the git rebase man page for some instructions at the end of the "Description" section. There is some related help on merging in the git user manual - see resolving a merge.

If you have not yet pushed this branch to github, you can carry on as normal, however if you have already pushed this commit see Push with force for how to replace your already published commits with the new ones.

Push with force#

If you have in some way re-written already pushed history (e.g. via Rewrite commit history or Rebase onto upstream/main) leaving you with a git history that looks something like

  A'--E cool-feature
 /
D---A---B---C origin/cool-feature

where you have pushed the commits A,B,C to your fork on GitHub (under the remote name origin) but now have the commits A' and E on your local branch cool-feature. If you try to push the new commits to GitHub, it will fail and show an error that looks like

$ git push
Pushing to github.com:origin/matplotlib.git
To github.com:origin/matplotlib.git
 ! [rejected]              cool_feature -> cool_feature (non-fast-forward)
error: failed to push some refs to 'github.com:origin/matplotlib.git'
hint: Updates were rejected because the tip of your current branch is behind
hint: its remote counterpart. Integrate the remote changes (e.g.
hint: 'git pull ...') before pushing again.
hint: See the 'Note about fast-forwards' in 'git push --help' for details.

If this push had succeeded, the commits A, B, and C would no longer be referenced by any branch and they would be discarded:

D---A'---E cool-feature, origin/cool-feature

By default git push helpfully tries to protect you from accidentally discarding commits by rejecting the push to the remote. When this happens, GitHub also adds the helpful suggestion to pull the remote changes and then try pushing again. In some cases, such as if you and a colleague are both committing and pushing to the same branch, this is a correct course of action.

However, in the case of having intentionally re-written history, we want to discard the commits on the remote and replace them with the new-and-improved versions from our local branch. In this case, what we want to do is

$ git push --force-with-lease

which tells git you are aware of the risks and want to do the push anyway. We recommend using --force-with-lease over the --force flag. The --force will do the push no matter what, whereas --force-with-lease will only do the push if the remote branch is where the local git client thought it was.

Be judicious with force-pushing. It is effectively re-writing published history, and if anyone has fetched the old commits, it will have a different view of history which can cause confusion.

Automated tests#

Whenever a pull request is created or updated, various automated test tools will run on all supported platforms and versions of Python.

  • Make sure the Linting, GitHub Actions, AppVeyor, CircleCI, and Azure pipelines are passing before merging (All checks are listed at the bottom of the GitHub page of your pull request). Here are some tips for finding the cause of the test failure:

    • If Linting fails, you have a code style issue, which will be listed as annotations on the pull request's diff.

    • If Mypy or Stubtest fails, you have inconsistency in type hints, which will be listed as annotations in the diff.

    • If a GitHub Actions or AppVeyor run fails, search the log for FAILURES. The subsequent section will contain information on the failed tests.

    • If CircleCI fails, likely you have some reStructuredText style issue in the docs. Search the CircleCI log for WARNING.

    • If Azure pipelines fail with an image comparison error, you can find the images as artifacts of the Azure job:

      • Click Details on the check on the GitHub PR page.

      • Click View more details on Azure Pipelines to go to Azure.

      • On the overview page artifacts are listed in the section Related.

  • Codecov and CodeQL are currently for information only. Their failure is not necessarily a blocker.

  • tox is not used in the automated testing. It is supported for testing locally.

  • If you know only a subset of CIs need to be run, this can be controlled on individual commits by including the following substrings in commit messages:

    • [ci doc]: restrict the CI to documentation checks. For when you only changed documentation (this skip is automatic if the changes are only under doc/ or galleries/).

    • [skip circle]: skip the documentation build check. For when you didn't change documentation.

    • Unit tests can be turned off for individual platforms with

      • [skip actions]: GitHub Actions

      • [skip appveyor] (must be in the first line of the commit): AppVeyor

      • [skip azp]: Azure Pipelines

    • [skip ci]: skip all CIs. Use this only if you know your changes do not need to be tested at all, which is very rare.