Sphinx Domains

What is a Domain?

Originally, Sphinx was conceived for a single project, the documentation of the Python language. Shortly afterwards, it was made available for everyone as a documentation tool, but the documentation of Python modules remained deeply built in – the most fundamental directives, like function, were designed for Python objects. Since Sphinx has become somewhat popular, interest developed in using it for many different purposes: C/C++ projects, JavaScript, or even reStructuredText markup (like in this documentation).

While this was always possible, it is now much easier to easily support documentation of projects using different programming languages or even ones not supported by the main Sphinx distribution, by providing a domain for every such purpose.

A domain is a collection of markup (reStructuredText directives and roles) to describe and link to objects belonging together, e.g. elements of a programming language. Directive and role names in a domain have names like domain:name, e.g. py:function. Domains can also provide custom indices (like the Python Module Index).

Having domains means that there are no naming problems when one set of documentation wants to refer to e.g. C++ and Python classes. It also means that extensions that support the documentation of whole new languages are much easier to write.

This section describes what the domains that come with Sphinx provide. The domain API is documented as well, in the section Domain API.

Basic Markup

Most domains provide a number of object description directives, used to describe specific objects provided by modules. Each directive requires one or more signatures to provide basic information about what is being described, and the content should be the description. The basic version makes entries in the general index; if no index entry is desired, you can give the directive option flag :noindex:. An example using a Python domain directive:

.. py:function:: spam(eggs)
                 ham(eggs)

   Spam or ham the foo.

This describes the two Python functions spam and ham. (Note that when signatures become too long, you can break them if you add a backslash to lines that are continued in the next line. Example:

.. py:function:: filterwarnings(action, message='', category=Warning, 
                                module='', lineno=0, append=False)
   :noindex:

(This example also shows how to use the :noindex: flag.)

The domains also provide roles that link back to these object descriptions. For example, to link to one of the functions described in the example above, you could say

The function :py:func:`spam` does a similar thing.

As you can see, both directive and role names contain the domain name and the directive name.

Default Domain

To avoid having to writing the domain name all the time when you e.g. only describe Python objects, a default domain can be selected with either the config value :confval:`primary_domain` or this directive:

.. default-domain:: name

Select a new default domain. While the :confval:`primary_domain` selects a global default, this only has an effect within the same file.

If no other default is selected, the Python domain (named py) is the default one, mostly for compatibility with documentation written for older versions of Sphinx.

Directives and roles that belong to the default domain can be mentioned without giving the domain name, i.e.

.. function:: pyfunc()

   Describes a Python function.

Reference to :func:`pyfunc`.

The Python Domain

The Python domain (name py) provides the following directives for module declarations:

.. py:module:: name

This directive marks the beginning of the description of a module (or package submodule, in which case the name should be fully qualified, including the package name). It does not create content (like e.g. py:class does).

This directive will also cause an entry in the global module index.

The platform option, if present, is a comma-separated list of the platforms on which the module is available (if it is available on all platforms, the option should be omitted). The keys are short identifiers; examples that are in use include “IRIX”, “Mac”, “Windows”, and “Unix”. It is important to use a key which has already been used when applicable.

The synopsis option should consist of one sentence describing the module’s purpose – it is currently only used in the Global Module Index.

The deprecated option can be given (with no value) to mark a module as deprecated; it will be designated as such in various locations then.

.. py:currentmodule:: name

This directive tells Sphinx that the classes, functions etc. documented from here are in the given module (like py:module), but it will not create index entries, an entry in the Global Module Index, or a link target for py:mod. This is helpful in situations where documentation for things in a module is spread over multiple files or sections – one location has the py:module directive, the others only py:currentmodule.

The following directives are provided for module and class contents:

.. py:data:: name

Describes global data in a module, including both variables and values used as “defined constants.” Class and object attributes are not documented using this environment.

.. py:exception:: name

Describes an exception class. The signature can, but need not include parentheses with constructor arguments.

.. py:function:: name(signature)

Describes a module-level function. The signature should include the parameters, enclosing optional parameters in brackets. Default values can be given if it enhances clarity; see Python Signatures. For example:

.. py:function:: Timer.repeat([repeat=3[, number=1000000]])

Object methods are not documented using this directive. Bound object methods placed in the module namespace as part of the public interface of the module are documented using this, as they are equivalent to normal functions for most purposes.

The description should include information about the parameters required and how they are used (especially whether mutable objects passed as parameters are modified), side effects, and possible exceptions. A small example may be provided.

.. py:class:: name[(signature)]

Describes a class. The signature can include parentheses with parameters which will be shown as the constructor arguments. See also Python Signatures.

Methods and attributes belonging to the class should be placed in this directive’s body. If they are placed outside, the supplied name should contain the class name so that cross-references still work. Example:

.. py:class:: Foo
   .. py:method:: quux()

-- or --

.. py:class:: Bar

.. py:method:: Bar.quux()

The first way is the preferred one.

.. py:attribute:: name

Describes an object data attribute. The description should include information about the type of the data to be expected and whether it may be changed directly.

.. py:method:: name(signature)

Describes an object method. The parameters should not include the self parameter. The description should include similar information to that described for function. See also Python Signatures.

.. py:staticmethod:: name(signature)

Like py:method, but indicates that the method is a static method.

New in version 0.4.

.. py:classmethod:: name(signature)

Like py:method, but indicates that the method is a class method.

New in version 0.6.

.. py:decorator:: name

.. py:decorator:: name(signature)

Describes a decorator function. The signature should not represent the signature of the actual function, but the usage as a decorator. For example, given the functions

def removename(func):
    func.__name__ = ''
    return func

def setnewname(name):
    def decorator(func):
        func.__name__ = name
        return func
    return decorator

the descriptions should look like this:

.. py:decorator:: removename

   Remove name of the decorated function.

.. py:decorator:: setnewname(name)

   Set name of the decorated function to *name*.

There is no py:deco role to link to a decorator that is marked up with this directive; rather, use the py:func role.

.. py:decoratormethod:: name

.. py:decoratormethod:: name(signature)

Same as py:decorator, but for decorators that are methods.

Refer to a decorator method using the py:meth role.

.. py:function:: compile(source[, filename[, symbol]])

.. py:function:: compile(source[, filename, symbol])

.. py:function:: compile(source : string[, filename, symbol]) -> ast object

.. py:function:: format_exception(etype, value, tb[, limit=None])

   Format the exception with a traceback.

   :param etype: exception type
   :param value: exception value
   :param tb: traceback object
   :param limit: maximum number of stack frames to show
   :type limit: integer or None
   :rtype: list of strings

:param integer limit: maximum number of stack frames to show

The C Domain

The C domain (name c) is suited for documentation of C API.

.. c:function:: type name(signature)

Describes a C function. The signature should be given as in C, e.g.:

.. c:function:: PyObject* PyType_GenericAlloc(PyTypeObject *type, Py_ssize_t nitems)

This is also used to describe function-like preprocessor macros. The names of the arguments should be given so they may be used in the description.

Note that you don’t have to backslash-escape asterisks in the signature, as it is not parsed by the reST inliner.

.. c:member:: type name

Describes a C struct member. Example signature:

.. c:member:: PyObject* PyTypeObject.tp_bases

The text of the description should include the range of values allowed, how the value should be interpreted, and whether the value can be changed. References to structure members in text should use the member role.

.. c:macro:: name

Describes a “simple” C macro. Simple macros are macros which are used for code expansion, but which do not take arguments so cannot be described as functions. This is not to be used for simple constant definitions. Examples of its use in the Python documentation include PyObject_HEAD and Py_BEGIN_ALLOW_THREADS.

.. c:type:: name

Describes a C type (whether defined by a typedef or struct). The signature should just be the type name.

.. c:var:: type name

Describes a global C variable. The signature should include the type, such as:

.. c:var:: PyObject* PyClass_Type

The C++ Domain

The C++ domain (name cpp) supports documenting C++ projects.

The following directives are available:

.. cpp:class:: signatures

.. cpp:function:: signatures

.. cpp:member:: signatures

.. cpp:type:: signatures

Describe a C++ object. Full signature specification is supported – give the signature as you would in the declaration. Here some examples:

.. cpp:function:: bool namespaced::theclass::method(int arg1, std::string arg2)

   Describes a method with parameters and types.

.. cpp:function:: bool namespaced::theclass::method(arg1, arg2)

   Describes a method without types.

.. cpp:function:: const T &array<T>::operator[]() const

   Describes the constant indexing operator of a templated array.

.. cpp:function:: operator bool() const

   Describe a casting operator here.

.. cpp:function:: constexpr void foo(std::string &bar[2]) noexcept

   Describe a constexpr function here.

.. cpp:member:: std::string theclass::name

.. cpp:member:: std::string theclass::name[N][M]

.. cpp:type:: theclass::const_iterator

Will be rendered like this:

bool namespaced::theclass::method(int arg1, std::string arg2)

Describes a method with parameters and types.

bool namespaced::theclass::method(arg1, arg2)

Describes a method without types.

const T &array<T>::operator[]() const

Describes the constant indexing operator of a templated array.

operator bool() const

Describe a casting operator here.

constexpr void foo(std::string &bar[2]) noexcept

Describe a constexpr function here.

std::string theclass::name

 

std::string theclass::name[N][M]

 

type theclass::const_iterator

 

.. cpp:namespace:: namespace

Select the current C++ namespace for the following objects.

These roles link to the given object types:

:cpp:class:

:cpp:func:

:cpp:member:

:cpp:type:

Reference a C++ object. You can give the full signature (and need to, for overloaded functions.)

Note

Sphinx’ syntax to give references a custom title can interfere with linking to template classes, if nothing follows the closing angle bracket, i.e. if the link looks like this: :cpp:class:`MyClass<T>`. This is interpreted as a link to T with a title of MyClass. In this case, please escape the opening angle bracket with a backslash, like this: :cpp:class:`MyClass<T>`.

The Standard Domain

The so-called “standard” domain collects all markup that doesn’t warrant a domain of its own. Its directives and roles are not prefixed with a domain name.

The standard domain is also where custom object descriptions, added using the add_object_type() API, are placed.

There is a set of directives allowing documenting command-line programs:

.. option:: name args, name args, ...

Describes a command line option or switch. Option argument names should be enclosed in angle brackets. Example:

.. option:: -m <module>, --module <module>

   Run a module as a script.

The directive will create a cross-reference target named after the first option, referencable by option (in the example case, you’d use something like :option:`-m`).

.. envvar:: name

Describes an environment variable that the documented code or program uses or defines. Referencable by envvar.

.. program:: name

Like py:currentmodule, this directive produces no output. Instead, it serves to notify Sphinx that all following option directives document options for the program called name.

If you use program, you have to qualify the references in your option roles by the program name, so if you have the following situation

.. program:: rm

.. option:: -r

   Work recursively.

.. program:: svn

.. option:: -r revision

   Specify the revision to work upon.

then :option:`rm -r` would refer to the first option, while :option:`svn -r` would refer to the second one.

The program name may contain spaces (in case you want to document subcommands like svn add and svn commit separately).

New in version 0.5.

There is also a very generic object description directive, which is not tied to any domain:

.. describe:: text

.. object:: text

This directive produces the same formatting as the specific ones provided by domains, but does not create index entries or cross-referencing targets. Example:

.. describe:: PAPER

   You can set this variable to select a paper size.

The JavaScript Domain

The JavaScript domain (name js) provides the following directives:

.. js:function:: name(signature)

Describes a JavaScript function or method. If you want to describe arguments as optional use square brackets as documented for Python signatures.

You can use fields to give more details about arguments and their expected types, errors which may be thrown by the function, and the value being returned:

.. js:function:: $.getJSON(href, callback[, errback])

   :param string href: An URI to the location of the resource.
   :param callback: Get's called with the object.
   :param errback:
       Get's called in case the request fails. And a lot of other
       text so we need multiple lines
   :throws SomeError: For whatever reason in that case.
   :returns: Something

This is rendered as:

$.getJSON(href, callback[, errback])

Arguments:	href (string) – An URI to the location of the resource. callback – Get’s called with the object. errback – Get’s called in case the request fails. And a lot of other text so we need multiple lines.
Throws SomeError:
	For whatever reason in that case.
Returns:	Something

.. js:class:: name

Describes a constructor that creates an object. This is basically like a function but will show up with a class prefix:

.. js:class:: MyAnimal(name[, age])

   :param string name: The name of the animal
   :param number age: an optional age for the animal

This is rendered as:

class MyAnimal(name[, age])

Arguments:	name (string) – The name of the animal age (number) – an optional age for the animal

.. js:data:: name

Describes a global variable or constant.

.. js:attribute:: object.name

Describes the attribute name of object.

These roles are provided to refer to the described objects:

:js:func:

:js:class:

:js:data:

:js:attr:

 

The reStructuredText domain

The reStructuredText domain (name rst) provides the following directives:

.. rst:directive:: name

Describes a reST directive. The name can be a single directive name or actual directive syntax (.. prefix and :: suffix) with arguments that will be rendered differently. For example:

.. rst:directive:: foo

   Foo description.

.. rst:directive:: .. bar:: baz

   Bar description.

will be rendered as:

.. foo::

Foo description.

.. bar:: baz

Bar description.

.. rst:role:: name

Describes a reST role. For example:

.. rst:role:: foo

   Foo description.

will be rendered as:

:foo:

Foo description.

These roles are provided to refer to the described objects:

:rst:dir:

:rst:role:

 

More domains

The sphinx-contrib repository contains more domains available as extensions; currently a Ruby and an Erlang domain.