Maintainer Information#

Releasing#

This section is about preparing a major/minor release, a release candidate (RC), or a bug-fix release. We follow PEP440 for the version scheme and to indicate different types of releases. Our convention is to follow the “major.minor.micro” scheme, although in practice there is no fundamental difference between major and minor releases and micro releases are bug-fix releases.

We adopted the following release schedule:

Major/Minor releases every 6 months, usually in May and November. These releases are numbered X.Y.0 and are preceded by one or more release candidates X.Y.0rcN.
Bug-fix releases are done as needed between major/minor releases and only apply to the last stable version. These releases are numbered X.Y.Z.

Preparation

Confirm that all blockers tagged for the milestone have been resolved, and that other issues tagged for the milestone can be postponed.
Make sure the deprecations, FIXMEs, and TODOs tagged for the release have been taken care of.
For major/minor final releases, make sure that a Release Highlights page has been done as a runnable example and check that its HTML rendering looks correct. It should be linked from the what’s new file for the new version of scikit-learn.

Permissions

The release manager must be a maintainer of the scikit-learn/scikit-learn repository to be able to publish on pypi.org and test.pypi.org (via a manual trigger of a dedicated Github Actions workflow).
The release manager must be a maintainer of the conda-forge/scikit-learn-feedstock repository to be able to publish on conda-forge. This can be changed by editing the recipe/meta.yaml file in the first release pull request.

Reference Steps#

Major/Minor RC

Suppose that we are preparing the release 1.6.0rc1.

The first RC ideally counts as a feature freeze. Each coming release candidate and the final release afterwards should include only minor documentation changes and bug fixes. Any major enhancement or new feature should be excluded.

Create the release branch 1.6.X directly in the main repository, where X is really the letter X, not a placeholder. The development for the final and subsequent bug-fix releases of 1.6 should also happen under this branch with different tags.
```
git fetch upstream main
git checkout upstream/main
git checkout -b 1.6.X
git push --set-upstream upstream 1.6.X
```

Create a PR targeting the 1.6.X branch. Copy the following release checklist to the description of this PR to track the progress.

* [ ] Update the sklearn dev0 version in main branch
* [ ] Set the version number in the release branch
* [ ] Check that the wheels for the release can be built successfully
* [ ] Merge the PR with `[cd build]` commit message to upload wheels to the staging repo
* [ ] Upload the wheels and source tarball to https://test.pypi.org
* [ ] Create tag on the main repo
* [ ] Confirm bot detected at https://github.com/conda-forge/scikit-learn-feedstock
      and wait for merge
* [ ] Upload the wheels and source tarball to PyPI
* [ ] Update news and what's new date in main branch
* [ ] Backport news and what's new date in release branch
* [ ] Announce on mailing list and on Twitter, and LinkedIn

Create a PR from main and targeting main to increment the dev0 __version__ variable in sklearn/__init__.py. This means while we are in the release candidate period, the latest stable is two version behind the main branch, instead of one. In this PR targeting main, you should also include a new what’s new file under the doc/whats_new/ directory so that we prepare the changelog for the next release.
In the release branch, change the version number __version__ in sklearn/__init__.py to 1.6.0rc1.
Trigger the wheel builder with the [cd build] commit marker. See also the workflow runs of the wheel builder.
```
git commit --allow-empty -m "[cd build] Trigger wheel builder workflow"
```
Note

The acronym CD in [cd build] stands for Continuous Delivery and refers to the automation used to generate the release artifacts (binary and source packages). This can be seen as an extension to CI which stands for Continuous Integration. The CD workflow on GitHub Actions is also used to automatically create nightly builds and publish packages for the development branch of scikit-learn. See also Installing nightly builds.
Once all the CD jobs have completed successfully in the PR, merge it with the [cd build] marker in the commit message. This time the results will be uploaded to the staging area. You should then be able to upload the generated artifacts (.tar.gz and .whl files) to https://test.pypi.org/ using the “Run workflow” form for the PyPI publishing workflow.

Warning

This PR should be merged with the rebase mode instead of the usual squash mode because we want to keep the history in the 1.6.X branch close to the history of the main branch which will help for future bug fix releases.

In addition if on merging, the last commit, containing the [cd build] marker, is empty, the CD jobs won’t be triggered. In this case, you can directly push a commit with the marker in the 1.6.X branch to trigger them.
If the steps above went fine, proceed with caution to create a new tag for the release. This should be done only when you are almost certain that the release is ready, since adding a new tag to the main repository can trigger certain automated processes.
```
git tag -a 1.6.0rc1  # in the 1.6.X branch
git push git@github.com:scikit-learn/scikit-learn.git 1.6.0rc1
```
Warning

Don’t use the github interface for publishing the release as a way to create the tag because it will automatically send notifications to all users that follow the repo even though the website isn’t updated and wheels aren’t uploaded yet.
Confirm that the bot has detected the tag on the conda-forge feedstock repository conda-forge/scikit-learn-feedstock. If not, submit a PR for the release, targeting the rc branch.
Trigger the PyPI publishing workflow again, but this time to upload the artifacts to the real https://pypi.org/. To do so, replace testpypi with pypi in the “Run workflow” form.

Alternatively, it is possible to collect locally the generated binary wheel packages and source tarball and upload them all to PyPI.
Uploading artifacts from local#
Check out at the release tag and run the following commands.
rm -r dist python -m pip install -U wheelhouse_uploader twine python -m wheelhouse_uploader fetch \ --version 1.6.0rc1 --local-folder dist scikit-learn \ https://pypi.anaconda.org/scikit-learn-wheels-staging/simple/scikit-learn/
These commands will download all the binary packages accumulated in the staging area on the anaconda.org hosting service and put them in your local ./dist folder. Check the contents of the ./dist folder: it should contain all the wheels along with the source tarball .tar.gz. Make sure you do not have developer versions or older versions of the scikit-learn package in that folder. Before uploading to PyPI, you can test uploading to test.pypi.org first.
twine upload --verbose --repository-url https://test.pypi.org/legacy/ dist/*
Then upload everything at once to pypi.org.
twine upload dist/*

Major/Minor Final

Suppose that we are preparing the release 1.6.0.

Create a new branch from the main branch, then start an interactive rebase from 1.6.X to select the commits that need to be backported:
```
git rebase -i upstream/1.6.X
```
This will open an interactive rebase with the git-rebase-todo containing all the latest commits on main. At this stage, you have to perform this interactive rebase with at least someone else (to not forget something and to avoid doubts).
- Do not remove lines but drop commit by replacing pick with drop.
- Commits to pick for a bug-fix release are generally prefixed with FIX, CI, and DOC. They should at least include all the commits of the merged PRs that were milestoned for this release.
- Commits to drop for a bug-fix release are generally prefixed with FEAT, MAINT, ENH, and API. Reasons for not including them is to prevent change of behavior (which should only happen in major/minor releases).
- After having dropped or picked commits, do not exit but paste the content of the git-rebase-todo message in the PR. This file is located at .git/rebase-merge/git-rebase-todo.
- Save and exit to start the interactive rebase. Resolve merge conflicts when necessary.

Create a PR targeting the 1.6.X branch. Copy the following release checklist to the description of this PR to track the progress.

* [ ] Set the version number in the release branch
* [ ] Check that the wheels for the release can be built successfully
* [ ] Merge the PR with `[cd build]` commit message to upload wheels to the staging repo
* [ ] Upload the wheels and source tarball to https://test.pypi.org
* [ ] Create tag on the main repo
* [ ] Confirm bot detected at https://github.com/conda-forge/scikit-learn-feedstock
      and wait for merge
* [ ] Upload the wheels and source tarball to PyPI
* [ ] Update news and what's new date in main branch
* [ ] Backport news and what's new date in release branch
* [ ] Update symlink for stable in https://github.com/scikit-learn/scikit-learn.github.io
* [ ] Publish to https://github.com/scikit-learn/scikit-learn/releases
* [ ] Announce on mailing list and on Twitter, and LinkedIn
* [ ] Update SECURITY.md in main branch

In the release branch, change the version number __version__ in sklearn/__init__.py to 1.6.0.
Trigger the wheel builder with the [cd build] commit marker. See also the workflow runs of the wheel builder.
```
git commit --allow-empty -m "[cd build] Trigger wheel builder workflow"
```
Note

The acronym CD in [cd build] stands for Continuous Delivery and refers to the automation used to generate the release artifacts (binary and source packages). This can be seen as an extension to CI which stands for Continuous Integration. The CD workflow on GitHub Actions is also used to automatically create nightly builds and publish packages for the development branch of scikit-learn. See also Installing nightly builds.
Once all the CD jobs have completed successfully in the PR, merge it with the [cd build] marker in the commit message. This time the results will be uploaded to the staging area. You should then be able to upload the generated artifacts (.tar.gz and .whl files) to https://test.pypi.org/ using the “Run workflow” form for the PyPI publishing workflow.

Warning

This PR should be merged with the rebase mode instead of the usual squash mode because we want to keep the history in the 1.6.X branch close to the history of the main branch which will help for future bug fix releases.

In addition if on merging, the last commit, containing the [cd build] marker, is empty, the CD jobs won’t be triggered. In this case, you can directly push a commit with the marker in the 1.6.X branch to trigger them.
If the steps above went fine, proceed with caution to create a new tag for the release. This should be done only when you are almost certain that the release is ready, since adding a new tag to the main repository can trigger certain automated processes.
```
git tag -a 1.6.0  # in the 1.6.X branch
git push git@github.com:scikit-learn/scikit-learn.git 1.6.0
```
Warning

Don’t use the github interface for publishing the release as a way to create the tag because it will automatically send notifications to all users that follow the repo even though the website isn’t updated and wheels aren’t uploaded yet.
Confirm that the bot has detected the tag on the conda-forge feedstock repository conda-forge/scikit-learn-feedstock. If not, submit a PR for the release, targeting the main branch.
Trigger the PyPI publishing workflow again, but this time to upload the artifacts to the real https://pypi.org/. To do so, replace testpypi with pypi in the “Run workflow” form.

Alternatively, it is possible to collect locally the generated binary wheel packages and source tarball and upload them all to PyPI.
Uploading artifacts from local#
Check out at the release tag and run the following commands.
rm -r dist python -m pip install -U wheelhouse_uploader twine python -m wheelhouse_uploader fetch \ --version 1.6.0 --local-folder dist scikit-learn \ https://pypi.anaconda.org/scikit-learn-wheels-staging/simple/scikit-learn/
These commands will download all the binary packages accumulated in the staging area on the anaconda.org hosting service and put them in your local ./dist folder. Check the contents of the ./dist folder: it should contain all the wheels along with the source tarball .tar.gz. Make sure you do not have developer versions or older versions of the scikit-learn package in that folder. Before uploading to PyPI, you can test uploading to test.pypi.org first.
twine upload --verbose --repository-url https://test.pypi.org/legacy/ dist/*
Then upload everything at once to pypi.org.
twine upload dist/*
In the main branch, edit the corresponding file in the doc/whats_new directory to update the release date, link the release highlights example, and add the list of contributor names. Suppose that the tag of the last release in the previous major/minor version is 1.5.2, then you can use the following command to retrieve the list of contributor names:
```
git shortlog -s 1.5.2.. |
  cut -f2- |
  sort --ignore-case |
  tr "\n" ";" |
  sed "s/;/, /g;s/, $//" |
  fold -s
```
Then cherry-pick it in the release branch.
In the main branch, edit doc/templates/index.html to change the “News” section in the landing page, along with the month of the release. Do not forget to remove old entries (two years or three releases ago) and update the “On-going development” entry. Then cherry-pick it in the release branch.

Update the symlink for stable and the latestStable variable in versionwarning.js in scikit-learn/scikit-learn.github.io.

cd /tmp
git clone --depth 1 --no-checkout git@github.com:scikit-learn/scikit-learn.github.io.git
cd scikit-learn.github.io
echo stable > .git/info/sparse-checkout
git checkout main
rm stable
ln -s 1.6 stable
sed -i "s/latestStable = '.*/latestStable = '1.6';/" versionwarning.js
git add stable versionwarning.js
git commit -m "Update stable to point to 1.6"
git push origin main

Publish the release at scikit-learn/scikit-learn and announce it on the mailing list and social networks. Remember to add a link to the changelog in the release note. Ideally, only perform this step once the package is available both on PyPI and conda-forge and once the website is up to date.
Update SECURITY.md to reflect the latest supported version 1.6.0.

Bug-fix

Suppose that we are preparing the release 1.5.3.

Create a new branch from the main branch, then start an interactive rebase from 1.5.X to select the commits that need to be backported:
```
git rebase -i upstream/1.5.X
```
This will open an interactive rebase with the git-rebase-todo containing all the latest commits on main. At this stage, you have to perform this interactive rebase with at least someone else (to not forget something and to avoid doubts).
- Do not remove lines but drop commit by replacing pick with drop.
- Commits to pick for a bug-fix release are generally prefixed with FIX, CI, and DOC. They should at least include all the commits of the merged PRs that were milestoned for this release.
- Commits to drop for a bug-fix release are generally prefixed with FEAT, MAINT, ENH, and API. Reasons for not including them is to prevent change of behavior (which should only happen in major/minor releases).
- After having dropped or picked commits, do not exit but paste the content of the git-rebase-todo message in the PR. This file is located at .git/rebase-merge/git-rebase-todo.
- Save and exit to start the interactive rebase. Resolve merge conflicts when necessary.

Create a PR targeting the 1.5.X branch. Copy the following release checklist to the description of this PR to track the progress.

* [ ] Set the version number in the release branch
* [ ] Check that the wheels for the release can be built successfully
* [ ] Merge the PR with `[cd build]` commit message to upload wheels to the staging repo
* [ ] Upload the wheels and source tarball to https://test.pypi.org
* [ ] Create tag on the main repo
* [ ] Confirm bot detected at https://github.com/conda-forge/scikit-learn-feedstock
      and wait for merge
* [ ] Upload the wheels and source tarball to PyPI
* [ ] Update news and what's new date in main branch
* [ ] Backport news and what's new date in release branch
* [ ] Publish to https://github.com/scikit-learn/scikit-learn/releases
* [ ] Announce on mailing list and on Twitter, and LinkedIn
* [ ] Update SECURITY.md in main branch

In the release branch, change the version number __version__ in sklearn/__init__.py to 1.5.3.
Trigger the wheel builder with the [cd build] commit marker. See also the workflow runs of the wheel builder.
```
git commit --allow-empty -m "[cd build] Trigger wheel builder workflow"
```
Note

The acronym CD in [cd build] stands for Continuous Delivery and refers to the automation used to generate the release artifacts (binary and source packages). This can be seen as an extension to CI which stands for Continuous Integration. The CD workflow on GitHub Actions is also used to automatically create nightly builds and publish packages for the development branch of scikit-learn. See also Installing nightly builds.
Once all the CD jobs have completed successfully in the PR, merge it with the [cd build] marker in the commit message. This time the results will be uploaded to the staging area. You should then be able to upload the generated artifacts (.tar.gz and .whl files) to https://test.pypi.org/ using the “Run workflow” form for the PyPI publishing workflow.

Warning

This PR should be merged with the rebase mode instead of the usual squash mode because we want to keep the history in the 1.5.X branch close to the history of the main branch which will help for future bug fix releases.

In addition if on merging, the last commit, containing the [cd build] marker, is empty, the CD jobs won’t be triggered. In this case, you can directly push a commit with the marker in the 1.5.X branch to trigger them.
If the steps above went fine, proceed with caution to create a new tag for the release. This should be done only when you are almost certain that the release is ready, since adding a new tag to the main repository can trigger certain automated processes.
```
git tag -a 1.5.3  # in the 1.5.X branch
git push git@github.com:scikit-learn/scikit-learn.git 1.5.3
```
Warning

Don’t use the github interface for publishing the release as a way to create the tag because it will automatically send notifications to all users that follow the repo even though the website isn’t updated and wheels aren’t uploaded yet.
Confirm that the bot has detected the tag on the conda-forge feedstock repository conda-forge/scikit-learn-feedstock. If not, submit a PR for the release, targeting the main branch.
Trigger the PyPI publishing workflow again, but this time to upload the artifacts to the real https://pypi.org/. To do so, replace testpypi with pypi in the “Run workflow” form.

Alternatively, it is possible to collect locally the generated binary wheel packages and source tarball and upload them all to PyPI.
Uploading artifacts from local#
Check out at the release tag and run the following commands.
rm -r dist python -m pip install -U wheelhouse_uploader twine python -m wheelhouse_uploader fetch \ --version 1.5.3 --local-folder dist scikit-learn \ https://pypi.anaconda.org/scikit-learn-wheels-staging/simple/scikit-learn/
These commands will download all the binary packages accumulated in the staging area on the anaconda.org hosting service and put them in your local ./dist folder. Check the contents of the ./dist folder: it should contain all the wheels along with the source tarball .tar.gz. Make sure you do not have developer versions or older versions of the scikit-learn package in that folder. Before uploading to PyPI, you can test uploading to test.pypi.org first.
twine upload --verbose --repository-url https://test.pypi.org/legacy/ dist/*
Then upload everything at once to pypi.org.
twine upload dist/*
In the main branch, edit the corresponding file in the doc/whats_new directory to update the release date and add the list of contributor names. Suppose that the tag of the last release in the previous major/minor version is 1.6.0, then you can use the following command to retrieve the list of contributor names:
```
git shortlog -s 1.6.0.. |
  cut -f2- |
  sort --ignore-case |
  tr "\n" ";" |
  sed "s/;/, /g;s/, $//" |
  fold -s
```
Then cherry-pick it in the release branch.
In the main branch, edit doc/templates/index.html to change the “News” section in the landing page, along with the month of the release. Then cherry-pick it in the release branch.
Publish the release at scikit-learn/scikit-learn and announce it on the mailing list and social networks. Remember to add a link to the changelog in the release note. Ideally, only perform this step once the package is available both on PyPI and conda-forge and once the website is up to date.
Update SECURITY.md to reflect the latest supported version 1.5.3.

Updating Authors List#

This section is about updating The people behind scikit-learn. First create a classic token on GitHub with the read:org permission. Then run the following script and enter the token when prompted:

cd build_tools
make authors  # Enter the token when prompted

Merging Pull Requests#

Individual commits are squashed when a PR is merged on GitHub. Before merging:

The resulting commit title can be edited if necessary. Note that this will rename the PR title by default.
The detailed description, containing the titles of all the commits, can be edited or deleted.
For PRs with multiple code contributors, care must be taken to keep the Co-authored-by: name <name@example.com> tags in the detailed description. This will mark the PR as having multiple co-authors. Whether code contributions are significantly enough to merit co-authorship is left to the maintainer’s discretion, same as for the what’s new entry.

The `scikit-learn.org` Website#

The scikit-learn website (https://scikit-learn.org) is hosted on GitHub, but should rarely be updated manually by pushing to the scikit-learn/scikit-learn.github.io repository. Most updates can be made by pushing to main (for /dev) or a release branch A.B.X, from which Circle CI builds and uploads the documentation automatically.

Experimental Features#

The sklearn.experimental module was introduced in 0.21 and contains experimental features and estimators that are subject to change without deprecation cycle.

To create an experimental module, refer to the contents of enable_halving_search_cv.py, or enable_iterative_imputer.py.

Note

These are permalinks as in 0.24, where these estimators are still experimental. They might be stable at the time of reading, hence the permalink. See below for instructions on the transition from experimental to stable.

Note that the public import path must be to a public subpackage (like sklearn/ensemble or sklearn/impute), not just a .py module. Also, the (private) experimental features that are imported must be in a submodule/subpackage of the public subpackage, e.g. sklearn/ensemble/_hist_gradient_boosting/ or sklearn/impute/_iterative.py. This is needed so that pickles still work in the future when the features aren’t experimental anymore.

To avoid type checker (e.g. mypy) errors a direct import of experimental estimators should be done in the parent module, protected by the if typing.TYPE_CHECKING check. See sklearn/ensemble/__init__.py, or sklearn/impute/__init__.py for an example. Please also write basic tests following those in test_enable_hist_gradient_boosting.py.

Make sure every user-facing code you write explicitly mentions that the feature is experimental, and add a # noqa comment to avoid PEP8-related warnings:

# To use this experimental feature, we need to explicitly ask for it
from sklearn.experimental import enable_iterative_imputer  # noqa
from sklearn.impute import IterativeImputer

For the docs to render properly, please also import enable_my_experimental_feature in doc/conf.py, otherwise sphinx will not be able to detect and import the corresponding modules. Note that using from sklearn.experimental import * does not work.

Note

Some experimental classes and functions may not be included in the sklearn.experimental module, e.g., sklearn.datasets.fetch_openml.

Once the feature becomes stable, remove all occurrences of enable_my_experimental_feature in the scikit-learn code base and make the enable_my_experimental_feature a no-op that just raises a warning, as in enable_hist_gradient_boosting.py. The file should stay there indefinitely as we do not want to break users’ code; we just incentivize them to remove that import with the warning. Also remember to update the tests accordingly, see test_enable_hist_gradient_boosting.py.