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If you need to make a backwards-incompatible change to a public API [1] that has been included in a release (e.g. deleting a method), then you must first deprecate the old behaviour in at least one release, before removing/updating it in the next major release.

Adding a Deprecation#

Removing a Public API#

The simplest form of deprecation occurs when you need to remove a public API. The public API in question is deprecated for a period before it is removed to allow time for user code to be updated. Sometimes the deprecation is accompanied by the introduction of a new public API.

Under these circumstances the following points apply:

  • Using the deprecated API must result in a concise deprecation warning which is an instance of iris.IrisDeprecation. It is easiest to call iris._deprecation.warn_deprecated(), which is a simple wrapper to warnings.warn() with the signature warn_deprecation(message, **kwargs).

  • Where possible, your deprecation warning should include advice on how to avoid using the deprecated API. For example, you might reference a preferred API, or more detailed documentation elsewhere.

  • You must update the docstring for the deprecated API to include a Sphinx deprecation directive:

    .. deprecated:: <VERSION>

    where you should replace <VERSION> with the major and minor version of Iris in which this API is first deprecated. For example: 1.8.

    As with the deprecation warning, you should include advice on how to avoid using the deprecated API within the content of this directive. Feel free to include more detail in the updated docstring than in the deprecation warning.

  • You should check the documentation for references to the deprecated API and update them as appropriate.

Changing a Default#

When you need to change the default behaviour of a public API the situation is slightly more complex. The recommended solution is to use the iris.FUTURE object. The iris.FUTURE object provides boolean attributes that allow user code to control at run-time the default behaviour of corresponding public APIs. When a boolean attribute is set to False it causes the corresponding public API to use its deprecated default behaviour. When a boolean attribute is set to True it causes the corresponding public API to use its new default behaviour.

The following points apply in addition to those for removing a public API:

  • You should add a new boolean attribute to iris.FUTURE (by modifying iris.Future) that controls the default behaviour of the public API that needs updating. The initial state of the new boolean attribute should be False. You should name the new boolean attribute to indicate that setting it to True will select the new default behaviour.

  • You should include a reference to this iris.FUTURE flag in your deprecation warning and corresponding Sphinx deprecation directive.

Removing a Deprecation#

When the time comes to make a new major release you should locate any deprecated APIs within the code that satisfy the one release minimum period described previously. Locating deprecated APIs can easily be done by searching for the Sphinx deprecation directives and/or deprecation warnings.

Removing a Public API#

The deprecated API should be removed and any corresponding documentation and/or example code should be removed/updated as appropriate.

Changing a Default#

  • You should update the initial state of the relevant boolean attribute of iris.FUTURE to True.

  • You should deprecate setting the relevant boolean attribute of iris.Future in the same way as described in Removing a Public API.