Usage (from a cloned CPython directory)

cherry_picker [--pr-remote REMOTE] [--upstream-remote REMOTE] [--dry-run] [--config-path CONFIG-PATH] [--status] [--abort/--continue] [--push/--no-push] [--auto-pr/--no-auto-pr] <commit_sha1> <branches>

Contents

• About
• Setup Info
• Cherry-picking 🐍🍒⛏️
  • Commit sha1
  • Options
  • Demo
  • Example
  • --pr-remote option
  • --upstream-remote option
  • --status option
  • --abort option
  • --continue option
  • --no-push option
  • --no-auto-pr option
  • --config-path option
• Creating Pull Requests
• Running Tests
• Publishing to PyPI
• Local installation
• Changelog

About

This tool is used to backport CPython changes from main into one or more of the maintenance branches (3.6, 3.5, 2.7).

cherry_picker can be configured to backport other projects with similar workflow as CPython. See the configuration file options below for more details.

The maintenance branch names should contain some sort of version number (X.Y). For example: 3.6, 3.5, 2.7, stable-2.6, 2.5-lts, are all supported branch names.

It will prefix the commit message with the branch, e.g. [3.6], and then opens up the pull request page.

Tests are to be written using pytest.

Setup Info

Requires Python 3.8+.

$ python3 -m venv venv
$ source venv/bin/activate
(venv) $ python -m pip install cherry_picker

The cherry picking script assumes that if an upstream remote is defined, then it should be used as the source of upstream changes and as the base for cherry-pick branches. Otherwise, origin is used for that purpose. You can override this behavior with the --upstream-remote option (e.g. --upstream-remote python to use a remote named python).

Verify that an upstream remote is set to the CPython repository:

$ git remote -v
...
upstream    https://github.com/python/cpython (fetch)
upstream    https://github.com/python/cpython (push)

If needed, create the upstream remote:

$ git remote add upstream https://github.com/python/cpython.git

By default, the PR branches used to submit pull requests back to the main repository are pushed to origin. If this is incorrect, then the correct remote will need be specified using the --pr-remote option (e.g. --pr-remote pr to use a remote named pr).

Cherry-picking 🐍🍒⛏️

(Setup first! See prev section)

From the cloned CPython directory:

(venv) $ cherry_picker [--pr-remote REMOTE] [--upstream-remote REMOTE] [--dry-run] [--config-path CONFIG-PATH] [--abort/--continue] [--status] [--push/--no-push] [--auto-pr/--no-auto-pr] <commit_sha1> <branches>

Commit sha1

The commit sha1 for cherry-picking is the squashed commit that was merged to the main branch. On the merged pull request, scroll to the bottom of the page. Find the event that says something like:

<coredeveloper> merged commit <commit_sha1> into python:main <sometime> ago.

By following the link to <commit_sha1>, you will get the full commit hash. Use the full commit hash for cherry_picker.py.

Options

--dry-run                 Dry Run Mode.  Prints out the commands, but not executed.
--pr-remote REMOTE        Specify the git remote to push into.  Default is 'origin'.
--upstream-remote REMOTE  Specify the git remote to use for upstream branches.
                          Default is 'upstream' or 'origin' if the former doesn't exist.
--status                  Do `git status` in cpython directory.

Additional options:

--abort        Abort current cherry-pick and clean up branch
--continue     Continue cherry-pick, push, and clean up branch
--no-push      Changes won't be pushed to remote
--no-auto-pr   PR creation page won't be automatically opened in the web browser or
               if GH_AUTH is set, the PR won't be automatically opened through API.
--config-path  Path to config file
               (`.cherry_picker.toml` from project root by default)

Configuration file example:

team = "aio-libs"
repo = "aiohttp"
check_sha = "f382b5ffc445e45a110734f5396728da7914aeb6"
fix_commit_msg = false
default_branch = "devel"

Available config options:

team            github organization or individual nick,
                e.g "aio-libs" for https://github.com/aio-libs/aiohttp
                ("python" by default)

repo            github project name,
                e.g "aiohttp" for https://github.com/aio-libs/aiohttp
                ("cpython" by default)

check_sha       A long hash for any commit from the repo,
                e.g. a sha1 hash from the very first initial commit
                ("7f777ed95a19224294949e1b4ce56bbffcb1fe9f" by default)

fix_commit_msg  Replace # with GH- in cherry-picked commit message.
                It is the default behavior for CPython because of external
                Roundup bug tracker (https://bugs.python.org) behavior:
                #xxxx should point on issue xxxx but GH-xxxx points
                on pull-request xxxx.
                For projects using GitHub Issues, this option can be disabled.

default_branch  Project's default branch name,
                e.g "devel" for https://github.com/ansible/ansible
                ("main" by default)

To customize the tool for used by other project:

1. Create a file called .cherry_picker.toml in the project's root folder (alongside with .git folder).
2. Add team, repo, fix_commit_msg, check_sha and default_branch config values as described above.
3. Use git add .cherry_picker.toml / git commit to add the config into git.
4. Add cherry_picker to development dependencies or install it by pip install cherry_picker
5. Now everything is ready, use cherry_picker <commit_sha> <branch1> <branch2> for cherry-picking changes from <commit_sha> into maintenance branches. Branch name should contain at least major and minor version numbers and may have some prefix or suffix. Only the first version-like substring is matched when the version is extracted from branch name.

Demo

• Installation: https://asciinema.org/a/125254
• Backport: https://asciinema.org/a/125256

Example

For example, to cherry-pick 6de2b7817f-some-commit-sha1-d064 into 3.5 and 3.6, run the following command from the cloned CPython directory:

(venv) $ cherry_picker 6de2b7817f-some-commit-sha1-d064 3.5 3.6

What this will do:

(venv) $ git fetch upstream

(venv) $ git checkout -b backport-6de2b78-3.5 upstream/3.5
(venv) $ git cherry-pick -x 6de2b7817f-some-commit-sha1-d064
(venv) $ git push origin backport-6de2b78-3.5
(venv) $ git checkout main
(venv) $ git branch -D backport-6de2b78-3.5

(venv) $ git checkout -b backport-6de2b78-3.6 upstream/3.6
(venv) $ git cherry-pick -x 6de2b7817f-some-commit-sha1-d064
(venv) $ git push origin backport-6de2b78-3.6
(venv) $ git checkout main
(venv) $ git branch -D backport-6de2b78-3.6

In case of merge conflicts or errors, the following message will be displayed:

Failed to cherry-pick 554626ada769abf82a5dabe6966afa4265acb6a6 into 2.7 :frowning_face:
... Stopping here.

To continue and resolve the conflict:
    $ cherry_picker --status  # to find out which files need attention
    # Fix the conflict
    $ cherry_picker --status  # should now say 'all conflict fixed'
    $ cherry_picker --continue

To abort the cherry-pick and cleanup:
    $ cherry_picker --abort

Passing the --dry-run option will cause the script to print out all the steps it would execute without actually executing any of them. For example:

$ cherry_picker --dry-run --pr-remote pr 1e32a1be4a1705e34011770026cb64ada2d340b5 3.6 3.5
Dry run requested, listing expected command sequence
fetching upstream ...
dry_run: git fetch origin
Now backporting '1e32a1be4a1705e34011770026cb64ada2d340b5' into '3.6'
dry_run: git checkout -b backport-1e32a1b-3.6 origin/3.6
dry_run: git cherry-pick -x 1e32a1be4a1705e34011770026cb64ada2d340b5
dry_run: git push pr backport-1e32a1b-3.6
dry_run: Create new PR: https://github.com/python/cpython/compare/3.6...ncoghlan:backport-1e32a1b-3.6?expand=1
dry_run: git checkout main
dry_run: git branch -D backport-1e32a1b-3.6
Now backporting '1e32a1be4a1705e34011770026cb64ada2d340b5' into '3.5'
dry_run: git checkout -b backport-1e32a1b-3.5 origin/3.5
dry_run: git cherry-pick -x 1e32a1be4a1705e34011770026cb64ada2d340b5
dry_run: git push pr backport-1e32a1b-3.5
dry_run: Create new PR: https://github.com/python/cpython/compare/3.5...ncoghlan:backport-1e32a1b-3.5?expand=1
dry_run: git checkout main
dry_run: git branch -D backport-1e32a1b-3.5

--pr-remote option

This will generate pull requests through a remote other than origin (e.g. pr)

--upstream-remote option

This will generate branches from a remote other than upstream/origin (e.g. python)

--status option

This will do git status for the CPython directory.

--abort option

Cancels the current cherry-pick and cleans up the cherry-pick branch.

--continue option

Continues the current cherry-pick, commits, pushes the current branch to origin, opens the PR page, and cleans up the branch.

--no-push option

Changes won't be pushed to remote. This allows you to test and make additional changes. Once you're satisfied with local changes, use --continue to complete the backport, or --abort to cancel and clean up the branch. You can also cherry-pick additional commits, by:

$ git cherry-pick -x <commit_sha1>

--no-auto-pr option

PR creation page won't be automatically opened in the web browser or if GH_AUTH is set, the PR won't be automatically opened through API. This can be useful if your terminal is not capable of opening a useful web browser, or if you use cherry-picker with a different Git hosting than GitHub.

--config-path option

Allows to override default config file path (<PROJ-ROOT>/.cherry_picker.toml) with a custom one. This allows cherry_picker to backport projects other than CPython.

Creating Pull Requests

When a cherry-pick was applied successfully, this script will open up a browser tab that points to the pull request creation page.

The url of the pull request page looks similar to the following:

https://github.com/python/cpython/compare/3.5...<username>:backport-6de2b78-3.5?expand=1

Press the Create Pull Request button.

Bedevere will then remove the needs backport to ... label from the original pull request against main.

Running Tests

Install pytest: pip install -U pytest

$ pytest

Tests require your local version of git to be 2.28.0+.

Publishing to PyPI

• See the release checklist.

Local installation

With flit installed, in the directory where pyproject.toml exists:

$ pip install

Changelog

See the changelog.