django/docs/misc/api-stability.txt

=============
API stability
=============

:doc:`The release of Django 1.0 </releases/1.0>` comes with a promise of API
stability and forwards-compatibility. In a nutshell, this means that code you
develop against Django 1.0 will continue to work against 1.1 unchanged, and you
should need to make only minor changes for any 1.X release.

What "stable" means
===================

In this context, stable means:

- All the public APIs -- everything documented in the linked documents below,
  and all methods that don't begin with an underscore -- will not be moved or
  renamed without providing backwards-compatible aliases.

- If new features are added to these APIs -- which is quite possible --
  they will not break or change the meaning of existing methods. In other
  words, "stable" does not (necessarily) mean "complete."

- If, for some reason, an API declared stable must be removed or replaced, it
  will be declared deprecated but will remain in the API for at least two
  minor version releases. Warnings will be issued when the deprecated method
  is called.

  See :ref:`official-releases` for more details on how Django's version
  numbering scheme works, and how features will be deprecated.

- We'll only break backwards compatibility of these APIs if a bug or
  security hole makes it completely unavoidable.

Stable APIs
===========

In general, everything covered in the documentation -- with the exception of
anything in the :doc:`internals area </internals/index>` is considered stable as
of 1.0. This includes these APIs:

- :doc:`Authorization </topics/auth>`

- :doc:`Caching </topics/cache>`.

- :doc:`Model definition, managers, querying and transactions
  </topics/db/index>`

- :doc:`Sending email </topics/email>`.

- :doc:`File handling and storage </topics/files>`

- :doc:`Forms </topics/forms/index>`

- :doc:`HTTP request/response handling </topics/http/index>`, including file
  uploads, middleware, sessions, URL resolution, view, and shortcut APIs.

- :doc:`Generic views </topics/class-based-views/index>`.

- :doc:`Internationalization </topics/i18n/index>`.

- :doc:`Pagination </topics/pagination>`

- :doc:`Serialization </topics/serialization>`

- :doc:`Signals </topics/signals>`

- :doc:`Templates </topics/templates>`, including the language, Python-level
  :doc:`template APIs </ref/templates/index>`, and :doc:`custom template tags
  and libraries </howto/custom-template-tags>`. We may add new template
  tags in the future and the names may inadvertently clash with
  external template tags. Before adding any such tags, we'll ensure that
  Django raises an error if it tries to load tags with duplicate names.

- :doc:`Testing </topics/testing/index>`

- :doc:`django-admin utility </ref/django-admin>`.

- :doc:`Built-in middleware </ref/middleware>`

- :doc:`Request/response objects </ref/request-response>`.

- :doc:`Settings </ref/settings>`. Note, though that while the :doc:`list of
  built-in settings </ref/settings>` can be considered complete we may -- and
  probably will -- add new settings in future versions. This is one of those
  places where "'stable' does not mean 'complete.'"

- :doc:`Built-in signals </ref/signals>`. Like settings, we'll probably add
  new signals in the future, but the existing ones won't break.

- :doc:`Unicode handling </ref/unicode>`.

- Everything covered by the :doc:`HOWTO guides </howto/index>`.

``django.utils``
----------------

Most of the modules in ``django.utils`` are designed for internal use. Only
the following parts of :doc:`django.utils </ref/utils>` can be considered stable:

- ``django.utils.cache``
- ``django.utils.datastructures.SortedDict`` -- only this single class; the
  rest of the module is for internal use.
- ``django.utils.encoding``
- ``django.utils.feedgenerator``
- ``django.utils.http``
- ``django.utils.safestring``
- ``django.utils.translation``
- ``django.utils.tzinfo``

Exceptions
==========

There are a few exceptions to this stability and backwards-compatibility
promise.

Security fixes
--------------

If we become aware of a security problem -- hopefully by someone following our
:ref:`security reporting policy <reporting-security-issues>` -- we'll do
everything necessary to fix it. This might mean breaking backwards compatibility; security trumps the compatibility guarantee.

Contributed applications (``django.contrib``)
---------------------------------------------

While we'll make every effort to keep these APIs stable -- and have no plans to
break any contrib apps -- this is an area that will have more flux between
releases. As the Web evolves, Django must evolve with it.

However, any changes to contrib apps will come with an important guarantee:
we'll make sure it's always possible to use an older version of a contrib app if
we need to make changes. Thus, if Django 1.5 ships with a backwards-incompatible
``django.contrib.flatpages``, we'll make sure you can still use the Django 1.4
version alongside Django 1.5. This will continue to allow for easy upgrades.

Historically, apps in ``django.contrib`` have been more stable than the core, so
in practice we probably won't have to ever make this exception. However, it's
worth noting if you're building apps that depend on ``django.contrib``.

APIs marked as internal
-----------------------

Certain APIs are explicitly marked as "internal" in a couple of ways:

- Some documentation refers to internals and mentions them as such. If the
  documentation says that something is internal, we reserve the right to
  change it.

- Functions, methods, and other objects prefixed by a leading underscore
  (``_``). This is the standard Python way of indicating that something is
  private; if any method starts with a single ``_``, it's an internal API.

.. _misc-api-stability-localflavor:

Local flavors
-------------

:mod:`django.contrib.localflavor` contains assorted pieces of code
that are useful for particular countries or cultures. This data is
local in nature, and is subject to change on timelines that will
almost never correlate with Django's own release schedules. For
example, a common change is to split a province into two new
provinces, or to rename an existing province.

These changes present two competing compatibility issues. Moving
forward, displaying the names of deprecated, renamed and dissolved
provinces in a selection widget is bad from a user interface
perspective. However, maintaining full backwards compatibility
requires that we support historical values that may be stored in a
database -- including values that may no longer be valid.

Therefore, Django has the following policy with respect to changes in
local flavor:

* At the time of a Django release, the data and algorithms
  contained in :mod:`django.contrib.localflavor` will, to the best
  of our ability, reflect the officially gazetted policies of the
  appropriate local government authority. If a province has been
  added, altered, or removed, that change will be reflected in
  Django's localflavor.

* These changes will *not* be backported to the previous stable
  release. Upgrading a minor version of Django should not require
  any data migration or audits for UI changes; therefore, if you
  want to get the latest province list, you will either need to
  upgrade your Django install, or backport the province list you
  need.

* For one release, the affected localflavor module will raise a
  ``RuntimeWarning`` when it is imported.

* The change will be announced in the release notes as a backwards
  incompatible change requiring attention. The change will also be
  annotated in the documentation for the localflavor module.

* Where necessary and feasible, a migration script will be provided
  to aid the migration process.

For example, Django 1.2 contains an Indonesian localflavor. It has a
province list that includes "Nanggroe Aceh Darussalam (NAD)" as a
province. The Indonesian government has changed the official name of
the province to "Aceh (ACE)". As a result, Django 1.3 does *not*
contain "Nanggroe Aceh Darussalam (NAD)" in the province list, but
*does* contain "Aceh (ACE)".