.. _documentation-guidelines:

*********************
Writing Documentation
*********************

High-quality, consistent documentation for astronomy code is one of the major
goals of the Astropy Project.  Hence, we describe our documentation procedures
and rules here.  For the astropy core project we try to keep to these as closely
as possible, while the standards for affiliated packages are somewhat looser.
(These procedures and guidelines are still recommended for affiliated packages,
as they encourage useful documentation, a characteristic often lacking in
professional astronomy software.)

Building the Documentation from source
======================================

For information about building the documentation from source, see
the :ref:`builddocs` section in the installation instructions.

Astropy Documentation Rules and Guidelines
==========================================

This section describes the standards for documentation format affiliated
packages that must follow for consideration of integration into the core
module, as well as the standard Astropy docstring format.

* All documentation text should follow the :ref:`astropy-style-guide`.

* All documentation should be written use the Sphinx documentation tool.

* The template package will provide a recommended general structure for
  documentation.

* Docstrings must be provided for all public classes, methods, and functions.

* Docstrings will be incorporated into the documentation using a version of
  numpydoc included with Astropy, and should follow the :doc:`docrules`.

* Examples and/or tutorials are strongly encouraged for typical use-cases of a
  particular module or class.

* Any external package dependencies aside from NumPy_, SciPy_, or Matplotlib_
  must be explicitly mentioned in the documentation. They should also be
  recorded in the ``setup.py`` file in the root of the astropy
  repository, optionally using an ``extras_require`` entry.

* Configuration options using the :mod:`astropy.config` mechanisms must be
  explicitly mentioned in the documentation.


The details of the docstring format are described on a separate page:

.. toctree::
    docrules


Sphinx Documentation Themes
===========================

An Astropy Project Sphinx HTML theme is included in the astropy-sphinx-theme_
package. This allows the theme to be used by both Astropy and affiliated
packages. The theme is activated by setting the theme in the global Astropy
sphinx configuration in sphinx-astropy_, which is imported in the sphinx
configuration of both Astropy and affiliated packages.

A different theme can be used by overriding a few sphinx
configuration variables set in the global configuration.

* To use a different theme, set ``html_theme`` to the name of a desired
  builtin Sphinx theme or a custom theme in ``package-name/docs/conf.py``
  (where ``'package-name'`` is "astropy" or the name of the affiliated
  package).

* To use a custom theme, additionally: place the theme in
  ``package-name/docs/_themes`` and add ``'_themes'`` to the
  ``html_theme_path`` variable. See the Sphinx_ documentation for more
  details on theming.

Sphinx extensions
=================

The documentation build process for Astropy uses a number of sphinx extensions
which are all installed automatically when installing sphinx-astropy_. These
facilitate easily documenting code in a homogeneous and readable way.

The main extensions used are:

* sphinx-automodapi_ - an extension
  that makes it easy to automatically generate API documentation.

* sphinx-gallery_ - an
  extension to generate example galleries

* numpydoc_ - an extension to parse
  docstrings in NumpyDoc format

In addition, the sphinx-astropy_ includes a few small extensions:

* ``sphinx_astropy.ext.edit_on_github`` - an extension to add 'Edit on GitHub'
  links to documentation pages.

* ``sphinx_astropy.ext.changelog_links`` - an extension to add links to
  pull requests when rendering the changelog.

* ``sphinx_astropy.ext.doctest`` - an extension that makes it possible to
  add metadata about doctests inside ``.rst`` files

Note that packages that make use of astropy-helpers_ have access to the::

    python setup.py build_docs

command. Provided that Sphinx is installed, the above command will temporarily
install sphinx-astropy_ and all its dependencies automatically.

.. _astropy-helpers: https://github.com/astropy/astropy-helpers
.. _NumPy: http://www.numpy.org/
.. _numpydoc: https://pypi.python.org/pypi/numpydoc/0.3.1
.. _Matplotlib: http://matplotlib.org/
.. _SciPy: https://www.scipy.org/
.. _Sphinx: http://sphinx.pocoo.org
.. _sphinx-automodapi: https://github.com/astropy/sphinx-automodapi
.. _astropy-sphinx-theme: https://github.com/astropy/astropy-sphinx-theme
.. _sphinx-astropy: https://github.com/astropy/sphinx-astropy
.. _sphinx-gallery: https://sphinx-gallery.readthedocs.io