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Git Development workflow

You’ve discovered a bug or something else you want to change in matplotlib .. — excellent!

You’ve worked out a way to fix it — even better!

You want to tell us about it — best of all!

The easiest way to contribute to matplotlib is through github. If for some reason you don’t want to use github, see Making patches for instructions on how to email patches to the mailing list.

You already have your own forked copy of the matplotlib repository, by following Making your own copy (fork) of matplotlib, Set up your fork, and you have configured git by following Configure git.

Workflow summary

  • Keep your master branch clean of edits that have not been merged to the main matplotlib development repo. Your master then will follow the main matplotlib repository.
  • Start a new feature branch for each set of edits that you do.
  • Do not merge the master branch or maintenance tracking branches into your feature branch. If you need to include commits from upstream branches (either to pick up a bug fix or to resolve a conflict) please rebase your branch on the upstream branch.
  • Ask for review!

This way of working really helps to keep work well organized, and in keeping history as clear as possible.

See — for example — linux git workflow.

Making a new feature branch

git checkout -b my-new-feature master

This will create and immediately check out a feature branch based on master. To create a feature branch based on a maintenance branch, use:

git fetch origin
git checkout -b my-new-feature origin/v1.0.x

Generally, you will want to keep this also 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 GitHub repo, called origin. You push up to your own repo on GitHub with:

git push origin my-new-feature

You will need to use this exact command, rather than simply git push every time you want to push changes on your feature branch to your GitHub repo. However, in git >1.7 you can set up a link by using the --set-upstream option:

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

and then next time you need to push changes to your branch a simple git push will suffice. Note that git push pushes out all branches that are linked to a remote branch.

The editing workflow


# hack hack
git add my_new_file
git commit -am 'NF - some message'
git push

In more detail

  1. Make some changes

  2. See which files have changed with git status (see 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")
  3. Check what the actual changes are with git diff (git diff).

  4. Add any new files to version control git add new_file_name (see git add).

  5. To commit all modified files into the local copy of your repo,, do git commit -am 'A commit message'. Note the -am options to commit. The m flag just signals that you’re going to type a message on the command line. The a flag — you can just take on faith — or see why the -a flag? — and the helpful use-case description in the tangled working copy problem. The git commit manual page might also be useful.

  6. To push the changes up to your forked repo on GitHub, do a git push (see git push).

Asking for code review — open a Pull Request (PR)

It’s a good idea to consult the Pull request checklist to make sure your pull request is ready for merging.

  1. Go to your repo URL — e.g.,
  2. Select your feature branch from the drop down menu:
  3. Click on the green button:
  4. Make sure that you are requesting a pull against the correct branch
  5. Enter a PR heading and description (if there is only one commit in the PR github will automatically fill these fields for you). If this PR is addressing a specific issue, please reference it by number (ex #1325) which github will automatically make into links.
  6. Click ‘Create Pull Request’ button!
  7. Discussion of the change will take place in the pull request thread.

Rebasing a Pull Request (PR)

When working on a PR, changes may occur in the parent branch (usually master). This can lead to conflict with changes in your branch. The conflicts can be trivial: for example both the parent branch and your branch add an entry to the top of CHANGELOG. Git can not unambiguously tell what to do with both changes (should one go above the other? if so, which order? should it try to merge them?) so it declares the branches can not be merged cleanly. GitHub can only automatically merge PR without conflicts, so you will need to manually ‘rebase’. This is the process of updating your branch with upstream changes, and resolving conflicts.

In git, rebasing is a mild form of re-writing history: it effectively forwards all your commits to the updated upstream commit. For a much more detailed explanation (with pictures!) see this nice write up. The NumPy team has also documented how to do this. In general, re-writing history, particularly published history, is considered bad practice, but in this case it is very useful.

The following example assumes that the remote of _your_ GitHub repository is called origin and the remote of the official repository is called matplotlib.

The first step is to make sure that your local copy of the upstream repository is up-to-date:

$ git fetch matplotlib

This updates your local copy of the repository, but does not change any files in your working copy. Next, switch to the branch that you want to update:

$ git checkout backend_plt_refactor

You are now ready to start the rebase of your branch onto the target parent branch, in this case matplotlib/master

$ git rebase matplotlib/master

and git will then give a bunch of feed back:

First, rewinding head to replay your work on top of it...
Applying: first steps to extract FigureManager* and friends from pyplot
Applying: split backend_qt4 into two parts, with and without Gcf
Applying: pep8 clean up on
Using index info to reconstruct a base tree...
M       lib/matplotlib/backends/
Falling back to patching base and 3-way merge...
Auto-merging lib/matplotlib/backends/
CONFLICT (content): Merge conflict in lib/matplotlib/backends/
Failed to merge in the changes.
Patch failed at 0013 pep8 clean up on
The copy of the patch that failed is found in:

When you have resolved this problem, run "git rebase --continue".
If you prefer to skip this patch, run "git rebase --skip" instead.
To check out the original branch and stop rebasing, run "git rebase --abort".

We see that a number of commits could be cleanly applied to the tip of matplotlib/master. However, git may eventually hit a commit that had conflicts: in the example above, this happens in the file lib/matplotlib/backends/ For more verbose information run

$ git status

You are currently rebasing branch 'backend_plt_refactor' on 'e6f8993'.
  (fix conflicts and then run "git rebase --continue")
  (use "git rebase --skip" to skip this patch)
  (use "git rebase --abort" to check out the original branch)

Unmerged paths:
  (use "git reset HEAD <file>..." to unstage)
  (use "git add <file>..." to mark resolution)

        both modified:      lib/matplotlib/backends/

no changes added to commit (use "git add" and/or "git commit -a")

This tells you exactly where the conflict (caused by the target branch and your commits modifying the same lines of code) is and provides some advice on how to proceed. Opening up the file in question, you will see blocks that look something like this:

<<<<<<< HEAD
        self.__dict__.clear()   # Is this needed? Other backends don't have it.
>>>>>>> pep8 clean up on

The block of code between <<<<<<< and ======= is the code on the target branch (in this case nothing) and the code between ======= and >>>>>>> is the code in the commit you are trying to rebase. The rest of the code is either the same or the diff can be unambiguously applied. You need to determine how to resolve the conflict (in this case, the code on HEAD is correct). Once you have resolved all the conflicts, add the file to the index:

$ git add lib/matplotlib/backends/

Repeat this for all of the files that have conflicts. When you are done with that you can check the status:

$ git status
rebase in progress; onto e6f8993
You are currently rebasing branch 'backend_plt_refactor' on 'e6f8993'.
  (all conflicts fixed: run "git rebase --continue")

Changes to be committed:
  (use "git reset HEAD <file>..." to unstage)

        modified:   lib/matplotlib/backends/

which shows us that we have resolved all of the conflicts with this commit and can continue:

$ git rebase --continue

You now iterate the until you have made it through all of the commits which have conflicts. Once you have successfully rebased your branch, be sure to re-run the tests to make sure everything is still working properly.

Your branch is now rebased, however, because of the way git determines the hash of each commit, it now shares no commits with your old branch published on GitHub so you can not push to that branch as you would when simply adding commits. In order to publish your newly rebased (and tested!) branch you need to use the --force flag:

$ git push --force origin

which will _replace_ all of the commits under your branch on GitHub with the new versions of the commit.

Congratulations, you have rebased your branch!

Staying up to date with changes in the central repository

This updates your working copy from the upstream matplotlib GitHub repo.


# go to your master branch
git checkout master
# pull changes from github
git fetch matplotlib
# merge from matplotlib
git merge --ff-only matplotlib/master

In detail

We suggest that you do this only for your master branch, and leave your ‘feature’ branches unmerged, to keep their history as clean as possible. This makes code review easier:

git checkout master

Make sure you have done Linking your repository to the upstream repo.

Merge the upstream code into your current development by first pulling the upstream repo to a copy on your local machine:

git fetch upstream

then merging into your current branch:

git merge --ff-only upstream/master

The --ff-only option guarantees that if you have mistakenly committed code on your master branch, the merge fails at this point. If you were to merge upstream/master to your master, you would start to diverge from the upstream. If this command fails, see the section on accidents.

The letters ‘ff’ in --ff-only mean ‘fast forward’, which is a special case of merge where git can simply update your branch to point to the other branch and not do any actual merging of files. For master and other integration branches this is exactly what you want.

Other integration branches

Some people like to keep separate local branches corresponding to the maintenance branches on GitHub. At the time of this writing, v1.0.x is the active maintenance branch. If you have such a local branch, treat is just as master: don’t commit on it, and before starting new branches off of it, update it from upstream:

git checkout v1.0.x
git fetch upstream
git merge --ff-only upstream/v1.0.x

But you don’t necessarily have to have such a branch. Instead, if you are preparing a bugfix that applies to the maintenance branch, fetch from upstream and base your bugfix on the remote branch:

git fetch upstream
git checkout -b my-bug-fix upstream/v1.0.x

Recovering from accidental commits on master

If you have accidentally committed changes on master and git merge --ff-only fails, don’t panic! First find out how much you have diverged:

git diff upstream/master...master

If you find that you want simply to get rid of the changes, reset your master branch to the upstream version:

git reset --hard upstream/master

As you might surmise from the words ‘reset’ and ‘hard’, this command actually causes your changes to the current branch to be lost, so think twice.

If, on the other hand, you find that you want to preserve the changes, create a feature branch for them:

git checkout -b my-important-changes

Now my-important-changes points to the branch that has your changes, and you can safely reset master as above — but make sure to reset the correct branch:

git checkout master
git reset --hard upstream/master

Deleting a branch on GitHub

git checkout master
# delete branch locally
git branch -D my-unwanted-branch
# delete branch on GitHub
git push origin :my-unwanted-branch

Note the colon : before my-unwanted-branch. See also:

Exploring 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

You can also look at the network graph visualizer for your GitHub repo.