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 Building documentation 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 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 Astropy Docstring Rules.
  • 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.
  • Configuration options using the astropy.config mechanisms must be explicitly mentioned in the documentation.

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

Sphinx Documentation Themes

A custom Sphinx HTML theme is included in the astropy source tree and installed along with astropy. This allows the theme to be used by default from both astropy and affiliated packages. This is done by setting the theme in the global astropy sphinx configuration, which is imported in the sphinx configuration of both astropy and affiliated packages.

Using a different theme for astropy or 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/ (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.

Adding more custom themes to astropy

Additional custom themes can be included in the astropy source tree by placing them in the directory astropy/astropy/sphinx/themes, and editing astropy/astropy/sphinx/ to include the theme (so that it is installed).

Sphinx extensions

Astropy includes a number of sphinx extensions that are used in astropy and its affiliated packages to facilitate easily documenting code in a homogeneous and readable way.

automodapi Extension

This sphinx extension adds a tools to simplify generating the API documentationfor Astropy packages and affiliated packages.

automodapi directive

This directive takes a single argument that must be module or package. It will produce a block of documentation that includes the docstring for the package, an automodsumm directive, and an automod-diagram if there are any classes in the module.

It accepts the following options:

  • :no-inheritance-diagram:

    If present, the inheritance diagram will not be shown even if the module/package has classes.

  • :skip: str

    This option results in the specified object being skipped, that is the object will not be included in the generated documentation. This option may appear any number of times to skip multiple objects.

  • :no-main-docstr:

    If present, the docstring for the module/package will not be generated. The function and class tables will still be used, however.

  • :headings: str

    Specifies the characters (in one string) used as the heading levels used for the generated section. This must have at least 2 characters (any after 2 will be ignored). This also must match the rest of the documentation on this page for sphinx to be happy. Defaults to “-^”, which matches the convention used for Python’s documentation, assuming the automodapi call is inside a top-level section (which usually uses ‘=’).

This extension also adds a sphinx configuration option automodapi_toctreedirnm. It must be a string that specifies the name of the directory the automodsumm generated documentation ends up in. This directory path should be relative to the documentation root (e.g., same place as index.rst). It defaults to ‘api’

automodsumm Extension

This sphinx extension adds two directives for summarizing the public members of a module or package.

These directives are primarily for use with the automodapi extension, but can be used independently.

automodsumm directive

This directive will produce an “autosummary”-style table for public attributes of a specified module. See the sphinx.ext.autosummary extension for details on this process. The main difference from the autosummary directive is that autosummary requires manually inputting all attributes that appear in the table, while this captures the entries automatically.

This directive requires a single argument that must be a module or package.

It also accepts any options supported by the autosummary directive- see sphinx.ext.autosummary for details. It also accepts two additional options:

  • :classes-only:

    If present, the autosummary table will only contain entries for classes. This cannot be used at the same time with :functions-only: .

  • :functions-only:

    If present, the autosummary table will only contain entries for functions. This cannot be used at the same time with :classes-only: .

  • :skip: obj1, [obj2, obj3, ...]

    If present, specifies that the listed objects should be skipped and not have their documentation generated, nor be includded in the summary table.

automod-diagram directive

This directive will produce an inheritance diagram like that of the sphinx.ext.inheritance_diagram extension.

This directive requires a single argument that must be a module or package. It accepts no options.


Like ‘inheritance-diagram’, ‘automod-diagram’ requires graphviz to generate the inheritance diagram.

edit_on_github Extension

This extension makes it easy to edit documentation on github.

It adds links associated with each docstring that go to the corresponding view source page on Github. From there, the user can push the “Edit” button, edit the docstring, and submit a pull request.

It has the following configuration options (to be set in the project’s

  • edit_on_github_project

    The name of the github project, in the form “username/projectname”.

  • edit_on_github_branch

    The name of the branch to edit. If this is a released version, this should be a git tag referring to that version. For a dev version, it often makes sense for it to be “master”. It may also be a git hash.

  • edit_on_github_source_root

    The location within the source tree of the root of the Python package. Defaults to “lib”.

  • edit_on_github_doc_root

    The location within the source tree of the root of the documentation source. Defaults to “doc”, but it may make sense to set it to “doc/source” if the project uses a separate source directory.

  • edit_on_github_docstring_message

    The phrase displayed in the links to edit a docstring. Defaults to “[edit on github]”.

  • edit_on_github_page_message

    The phrase displayed in the links to edit a RST page. Defaults to “[edit this page on github]”.

  • edit_on_github_help_message

    The phrase displayed as a tooltip on the edit links. Defaults to “Push the Edit button on the next page”

  • edit_on_github_skip_regex

    When the path to the .rst file matches this regular expression, no “edit this page on github” link will be added. Defaults to "_.*".

numpydoc Extension

This extension (and some related extensions) are a port of the numpydoc extension written by the NumPy and SciPy, projects, with some tweaks for Astropy. Its main purposes is to reprocess docstrings from code into a form sphinx understands. Generally, there’s no need to interact with it directly, as docstrings following the doc:docrules will be processed automatically.

Other Extensions

astropy.spinx.ext includes a few other extensions that are primarily helpers for the other extensions or workarounds for undesired behavior. Their APIs are not included here because we may change them in the future.