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Developing a "Hello world" extension
====================================
The objective of this tutorial is to create a very basic extension that adds a
new directive. This directive will output a paragraph containing "hello world".
Only basic information is provided in this tutorial. For more information, refer
to the :doc:`other tutorials <index>` that go into more details.
.. warning::
For this extension, you will need some basic understanding of docutils_
and Python.
Overview
--------
We want the extension to add the following to Sphinx:
* A ``helloworld`` directive, that will simply output the text "hello world".
Prerequisites
-------------
We will not be distributing this plugin via `PyPI`_ and will instead include it
as part of an existing project. This means you will need to use an existing
project or create a new one using :program:`sphinx-quickstart`.
We assume you are using separate source (:file:`source`) and build
(:file:`build`) folders. Your extension file could be in any folder of your
project. In our case, let's do the following:
#. Create an :file:`_ext` folder in :file:`source`
#. Create a new Python file in the :file:`_ext` folder called
:file:`helloworld.py`
Here is an example of the folder structure you might obtain:
.. code-block:: text
└── source
├── _ext
│ └── helloworld.py
├── _static
├── conf.py
├── somefolder
├── index.rst
├── somefile.rst
└── someotherfile.rst
Writing the extension
---------------------
Open :file:`helloworld.py` and paste the following code in it:
.. literalinclude:: examples/helloworld.py
:language: python
:linenos:
Some essential things are happening in this example, and you will see them for
all directives.
.. rubric:: The directive class
Our new directive is declared in the ``HelloWorld`` class.
.. literalinclude:: examples/helloworld.py
:language: python
:linenos:
:lines: 5-9
This class extends the docutils_' ``Directive`` class. All extensions that
create directives should extend this class.
.. seealso::
`The docutils documentation on creating directives <docutils directives_>`_
This class contains a ``run`` method. This method is a requirement and it is
part of every directive. It contains the main logic of the directive and it
returns a list of docutils nodes to be processed by Sphinx. These nodes are
docutils' way of representing the content of a document. There are many types of
nodes available: text, paragraph, reference, table, etc.
.. seealso::
`The docutils documentation on nodes <docutils nodes_>`_
The ``nodes.paragraph`` class creates a new paragraph node. A paragraph
node typically contains some text that we can set during instantiation using
the ``text`` parameter.
.. rubric:: The ``setup`` function
.. currentmodule:: sphinx.application
This function is a requirement. We use it to plug our new directive into
Sphinx.
.. literalinclude:: examples/helloworld.py
:language: python
:linenos:
:lines: 12-
The simplest thing you can do is to call the :meth:`~Sphinx.add_directive` method,
which is what we've done here. For this particular call, the first argument is
the name of the directive itself as used in a reST file. In this case, we would
use ``helloworld``. For example:
.. code-block:: rst
Some intro text here...
.. helloworld::
Some more text here...
We also return the :ref:`extension metadata <ext-metadata>` that indicates the
version of our extension, along with the fact that it is safe to use the
extension for both parallel reading and writing.
Using the extension
-------------------
The extension has to be declared in your :file:`conf.py` file to make Sphinx
aware of it. There are two steps necessary here:
#. Add the :file:`_ext` directory to the `Python path`_ using
``sys.path.append``. This should be placed at the top of the file.
#. Update or create the :confval:`extensions` list and add the extension file
name to the list
For example:
.. code-block:: python
import os
import sys
sys.path.append(os.path.abspath("./_ext"))
extensions = ['helloworld']
.. tip::
We're not distributing this extension as a `Python package`_, we need to
modify the `Python path`_ so Sphinx can find our extension. This is why we
need the call to ``sys.path.append``.
You can now use the extension in a file. For example:
.. code-block:: rst
Some intro text here...
.. helloworld::
Some more text here...
The sample above would generate:
.. code-block:: text
Some intro text here...
Hello World!
Some more text here...
Further reading
---------------
This is the very basic principle of an extension that creates a new directive.
For a more advanced example, refer to :doc:`todo`.
.. _docutils: https://docutils.sourceforge.io/
.. _docutils directives: https://docutils.sourceforge.io/docs/howto/rst-directives.html
.. _docutils nodes: https://docutils.sourceforge.io/docs/ref/doctree.html
.. _PyPI: https://pypi.org/
.. _Python package: https://packaging.python.org/
.. _Python path: https://docs.python.org/3/using/cmdline.html#envvar-PYTHONPATH
|
