API stability

The release of Django 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 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 internals area is considered stable as of 1.0. This includes these APIs:

django.utils

Most of the modules in django.utils are designed for internal use. Only the following parts of django.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 security reporting policy – 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.

Local flavors

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 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)”.

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