17. Development Cycle

The responsibilities of a core developer shift based on what kind of branch of Python a developer is working on and what stage the branch is in.

To clarify terminology, Python uses a major.minor.micro nomenclature for production-ready releases. So for Python 3.1.2 final, that is a major version of 3, a minor version of 1, and a micro version of 2.

• new major versions are exceptional; they only come when strongly incompatible changes are deemed necessary, and are planned very long in advance;

• new minor versions are feature releases; they get released annually, from the current in-development branch;

• new micro versions are bugfix releases; they get released roughly every 2 months; they are prepared in maintenance branches.

We also publish non-final versions which get an additional qualifier: Alpha, Beta, release candidate. These versions are aimed at testing by advanced users, not production use.

Each release of Python is tagged in the source repo with a tag of the form vX.Y.ZTN, where X is the major version, Y is the minor version, Z is the micro version, T is the release level (a for alpha releases, b for beta, rc release candidate, and null for final releases), and N is the release serial number. Some examples of release tags: v3.7.0a1, v3.6.3, v2.7.14rc1.

17.1. Branches

There is a branch for each feature version, whether released or not (e.g. 3.7, 3.8).

17.1.1. In-development (main) branch

The main branch is the branch for the next feature release; it is under active development for all kinds of changes: new features, semantic changes, performance improvements, bug fixes.

At some point during the life-cycle of a release, a new maintenance branch is created to host all bug fixing activity for further micro versions in a feature version (3.8.1, 3.8.2, etc.).

For versions 3.4 and before, this was conventionally done when the final release was cut (for example, 3.4.0 final).

Starting with the 3.5 release, we create the release maintenance branch (e.g. 3.5) at the time we enter beta (3.5.0 beta 1). This allows feature development for the release 3.n+1 to occur within the main branch alongside the beta and release candidate stabilization periods for release 3.n.

17.1.2. Maintenance branches

A branch for a previous feature release, currently being maintained for bug fixes, or for the next feature release in its beta or release candidate stages. There is usually either one or two maintenance branches at any given time for Python 3.x. After the final release of a new minor version (3.x.0), releases produced from a maintenance branch are called bugfix or maintenance releases; the terms are used interchangeably. These releases have a micro version number greater than zero.

The only changes allowed to occur in a maintenance branch without debate are bug fixes. Also, a general rule for maintenance branches is that compatibility must not be broken at any point between sibling micro releases (3.5.1, 3.5.2, etc.). For both rules, only rare exceptions are accepted and must be discussed first.

A new maintenance branch is normally created when the next feature release cycle reaches feature freeze, i.e. at its first beta pre-release. From that point on, changes intended for remaining pre-releases, the final release (3.x.0), and subsequent bugfix releases are merged to that maintenance branch.

Sometime following the final release (3.x.0), the maintenance branch for the previous minor version will go into security mode, usually after at least one more bugfix release at the discretion of the release manager. For example, the 3.4 maintenance branch was put into security mode after the 3.4.4 bugfix release which followed the release of 3.5.1.

17.1.3. Security branches

A branch less than 5 years old but no longer in bugfix mode is a security branch.

The only changes made to a security branch are those fixing issues exploitable by attackers such as crashes, privilege escalation and, optionally, other issues such as denial of service attacks. Any other changes are not considered a security risk and thus not backported to a security branch. You should also consider fixing hard-failing tests in open security branches since it is important to be able to run the tests successfully before releasing.

Commits to security branches are to be coordinated with the release manager for the corresponding feature version, as listed in the Status of Python branches. Merging of pull requests to security branches is restricted to release managers. Any release made from a security branch is source-only and done only when actual security patches have been applied to the branch. These releases have a micro version number greater than the last bugfix release.

17.1.4. End-of-life branches

The code base for a release cycle which has reached end-of-life status is frozen and no longer has a branch in the repo. The final state of the end-of-lifed branch is recorded as a tag with the same name as the former branch, e.g. 3.3 or 2.6.

For reference, here are the Python versions that most recently reached their end-of-life:

The latest release for each Python version can be found on the download page.

17.2. Stages

Based on what stage the in-development version of Python is in, the responsibilities of a core developer change in regards to commits to the VCS.

17.2.1. Pre-alpha

The branch is in this stage when no official release has been done since the latest final release. There are no special restrictions placed on commits, although the usual advice applies (getting patches reviewed, avoiding breaking the buildbots).

17.2.2. Alpha

Alpha releases typically serve as a reminder to core developers that they need to start getting in changes that change semantics or add something to Python as such things should not be added during a Beta. Otherwise no new restrictions are in place while in alpha.

17.2.3. Beta

After a first beta release is published, no new features are accepted. Only bug fixes and improvements to documentation and tests can now be committed. This is when core developers should concentrate on the task of fixing regressions and other new issues filed by users who have downloaded the alpha and beta releases.

Being in beta can be viewed much like being in RC but without the extra overhead of needing commit reviews.

Please see the note in the In-development (main) branch section above for new information about the creation of the 3.5 maintenance branch during beta.

17.2.4. Release Candidate (RC)

A branch preparing for an RC release can only have bugfixes applied that have been reviewed by other core developers. Generally, these issues must be severe enough (e.g. crashes) that they deserve fixing before the final release. All other issues should be deferred to the next development cycle, since stability is the strongest concern at this point.

While the goal is to have no code changes between a RC and a final release, there may be a need for final documentation or test fixes. Any such proposed changes should be discussed first with the release manager.

You cannot skip the peer review during an RC, no matter how small! Even if it is a simple copy-and-paste change, everything requires peer review from a core developer.

17.2.5. Final

When a final release is being cut, only the release manager (RM) can make changes to the branch. After the final release is published, the full development cycle starts again for the next minor version.

17.3. Repository Administration

The source code is currently hosted on GitHub in the Python organization.

17.3.1. Organization Repository Policy

Within the Python organization, repositories are expected to fall within these general categories:

1. The reference implementation of Python and related repositories (i.e. CPython)

2. Reference implementations of PEPs (e.g. mypy)

3. Tooling and support around CPython and the language (e.g. python.org repository)

4. PSF-related repositories (e.g. the Code of Conduct)

5. PSF Infrastructure repositories (e.g. the PSF Infrastructure Salt configurations)

For any repository which does not explicitly and clearly fall under one of these categories, permission should be sought from the Python steering council.

17.3.2. Organization Owner Policy

The GitHub Organization Owner role allows for full management of all aspects of the Python organization. Allowing for visibility and management of all aspects at all levels including organization membership, team membership, access control, and merge privileges on all repositories. For full details of the permission levels see GitHub’s documentation on Organization permission levels. This role is paramount to the security of the Python Language, Community, and Infrastructure.

The Executive Director of the Python Software Foundation delegates authority on GitHub Organization Owner Status to Ee W. Durbin III - Python Software Foundation Director of Infrastructure. Common reasons for this role are: Infrastructure Staff Membership, Python Software Foundation General Counsel, and Python Software Foundation Staff as fallback.

Inactive or unreachable members may be removed with or without notice. Members who no longer necessitate this level of access will be removed with notice.

Multi-Factor Authentication must be enabled by the user in order to remain an Owner of the Python Organization.

17.3.3. Current Owners

17.3.4. Repository Administrator Role Policy

The Administrator role on the repository allows for managing all aspects including collaborators, access control, integrations, webhooks, and branch protection. For full details of the permission levels see GitHub’s documentation on Repository permission levels. Common reasons for this role are: maintenance of Core Developer Workflow tooling, Release Managers for all in-development, maintenance, and security mode releases, and additional Python Core Developers as necessary for redundancy. Occasional temporary administrator access is acceptable as necessary for Core Developer workflow projects.

Inactive or unreachable members may be removed with or without notice. Members who no longer necessitate this level of access will be removed with notice.

Multi-Factor Authentication must be enabled by the user in order to remain an Administrator of the repository.

17.3.5. Current Administrators

17.3.6. Repository Release Manager Role Policy

Release Managers for in-development, maintenance, and security mode Python releases are granted Administrator privileges on the repository. Once a release branch has entered end-of-life, the Release Manager for that branch is removed as an Administrator and granted sole privileges (out side of repository administrators) to merge changes to that branch.

Multi-Factor Authentication must be enabled by the user in order to retain access as a Release Manager of the branch.