doc/extdev/index.rst
.. _dev-extensions:
Since many projects will need special features in their documentation, Sphinx is designed to be extensible on several levels.
Here are a few things you can do in an extension:
builder\s to support new output formats or actions on the
parsed documents.markupapi.events.An extension is simply a Python module with a setup() function. A user
activates the extension by placing the extension's module name
(or a sub-module) in their :confval:extensions configuration value.
When :program:sphinx-build is executed, Sphinx will attempt to import each
module that is listed, and execute yourmodule.setup(app). This
function is used to prepare the extension (e.g., by executing Python code),
linking resources that Sphinx uses in the build process (like CSS or HTML
files), and notifying Sphinx of everything the extension offers (such
as directive or role definitions). The app argument is an instance of
:class:.Sphinx and gives you control over most aspects of the Sphinx build.
.. note::
The configuration file itself can be treated as an extension if it
contains a ``setup()`` function. All other extensions to load must be
listed in the :confval:`extensions` configuration value.
The rest of this page describes some high-level aspects of developing
extensions and various parts of Sphinx's behavior that you can control.
For some examples of how extensions can be built and used to control different
parts of Sphinx, see the :ref:extension-tutorials-index.
.. _important-objects:
There are several key objects whose API you will use while writing an extension. These are:
Application
The application object (usually called app) is an instance of
:class:.Sphinx.
It controls most high-level functionality, such as loading config,
initialising the environment, and the setup of extensions.
Environment
The build environment object (usually called env) is an instance of
:class:.BuildEnvironment. It is responsible for parsing the source
documents, stores all metadata about the document collection and is
serialized to disk after each build.
Its API provides methods to do with access to metadata, resolving references, etc. It can also be used by extensions to cache information that should persist for incremental rebuilds.
If you have the application or builder object, the environment is available
as app.env or builder.env.
In :class:.SphinxDirective, :class:.SphinxRole, or :class:.SphinxTransform
subclasses, the environment is available as self.env.
Builder
The builder object (usually called builder) is an instance of a specific
subclass of :class:.Builder. Each builder class knows how to convert the
parsed documents into an output format, or otherwise process them (e.g. check
external links).
If you have the application object, the builder is available as
app.builder.
Config
The config object (usually called config) provides the values of
configuration values set in :file:conf.py as attributes. It is an instance
of :class:.Config.
The config is available as env.config, builder.config, or app.config.
In :class:.SphinxDirective, :class:.SphinxRole, or :class:.SphinxTransform
subclasses, the environment is available as self.config.
Events
The event manager object (usually called events) manages and dispatches
Sphinx's events system.
It is an instance of :class:.EventManager.
The event manager is available as env.events, builder.events,
or app.events.
To see an example of use of these objects, refer to
:ref:the tutorials <extension-tutorials-index>.
.. _build-phases:
One thing that is vital in order to understand extension mechanisms is the way in which a Sphinx project is built: this works in several phases.
.. graphviz:: /_static/diagrams/sphinx_build_phases.dot :caption: Build phases
Phase 0: Initialization
In this phase, almost nothing of interest to us happens. The source directory is searched for source files, and extensions are initialized. Should a stored build environment exist, it is loaded, otherwise a new one is created.
Phase 1: Reading
In Phase 1, all source files (and on subsequent builds, those that are new or changed) are read and parsed. This is the phase where directives and roles are encountered by docutils, and the corresponding code is executed. The output of this phase is a doctree for each source file; that is a tree of docutils nodes. For document elements that aren't fully known until all existing files are read, temporary nodes are created.
There are nodes provided by docutils, which are documented in the docutils documentation <https://docutils.sourceforge.io/docs/ref/doctree.html>__.
Additional nodes are provided by Sphinx and :ref:documented here <nodes>.
During reading, the build environment is updated with all meta- and cross reference data of the read documents, such as labels, the names of headings, described Python objects and index entries. This will later be used to replace the temporary nodes.
The parsed doctrees are stored on the disk, because it is not possible to hold all of them in memory.
Phase 2: Consistency checks
Some checking is done to ensure no surprises in the built documents.
Phase 3: Resolving
Now that the metadata and cross-reference data of all existing documents is known, all temporary nodes are replaced by nodes that can be converted into output using components called transforms. For example, links are created for object references that exist, and simple literal nodes are created for those that don't.
Phase 4: Writing
This phase converts the resolved doctrees to the desired output format, such as HTML or LaTeX. This happens via a so-called docutils writer that visits the individual nodes of each doctree and produces some output in the process.
.. note::
Some builders deviate from this general build plan, for example, the builder that checks external links does not need anything more than the parsed doctrees and therefore does not have phases 2--4.
To see an example of application, refer to :ref:tutorial-extend-build.
.. _ext-metadata:
.. versionadded:: 1.3
The setup() function should return a dictionary.
This is treated by Sphinx as metadata of the extension.
Metadata keys currently recognized are:
'version'
A string that identifies the extension version.
It is used for extension version requirement checking
(see :confval:needs_extensions) and informational purposes.
If no version string is returned, 'unknown version' is used by default.
'env_version'
A non-zero positive integer integer that records
the version of data stored in the environment by the extension.
.. attention::
If 'env_version' is not set, the extension must not
store any data or state directly on the environment object (env).
This key must be defined if the extension uses the env object to store data.
The version number must be incremented whenever the type, structure, or meaning
of the stored data change, to ensure Sphinx does not try and load invalid data
from a cached environment.
.. versionadded:: 1.8
'parallel_read_safe'
A boolean that specifies if parallel reading of source files
can be used when the extension is loaded.
It defaults to False, meaning that you have to explicitly specify
your extension to be safe for parallel reading after checking that it is.
.. important::
When *parallel-read-safe* is ``True``,
the extension must satisfy the following conditions:
* The core logic of the extension is parallelly executable during
the reading phase.
* It has event handlers for :event:`env-merge-info` and
:event:`env-purge-doc` events if it stores data to the build
environment object (``env``) during the reading phase.
'parallel_write_safe'
A boolean that specifies if parallel writing of output files
can be used when the extension is loaded.
Since extensions usually don't negatively influence the process,
this defaults to True.
.. important::
When *parallel-write-safe* is ``True``,
the extension must satisfy the following conditions:
* The core logic of the extension is parallelly executable during
the writing phase.
These sections provide a more complete description of the tools at your
disposal when developing Sphinx extensions. Some are core to Sphinx
(such as the :doc:appapi) while others trigger specific behavior
(such as the :doc:i18n)
.. toctree:: :maxdepth: 2
appapi event_callbacks projectapi envapi builderapi eventapi collectorapi markupapi domainapi parserapi nodes logging i18n utils testing deprecated