.. _developing_modules_documenting:
.. _module_documenting:

*******************************
Module format and documentation
*******************************

If you want to contribute your module to Ansible, you must write your module in Python and follow the standard format described below. (Unless you're writing a Windows module, in which case the :ref:`Windows guidelines <developing_modules_general_windows>` apply.) In addition to following this format, you should review our :ref:`submission checklist <developing_modules_checklist>`, :ref:`programming tips <developing_modules_best_practices>`, and :ref:`strategy for maintaining Python 2 and Python 3 compatibility <developing_python_3>`, as well as information about :ref:`testing <developing_testing>` before you open a pull request.

Every Ansible module written in Python must begin with seven standard sections in a particular order, followed by the code. The sections in order are:

.. contents::
   :depth: 1
   :local:

.. note:: Why don't the imports go first?

  Keen Python programmers may notice that contrary to PEP 8's advice we don't put ``imports`` at the top of the file. This is because the ``ANSIBLE_METADATA`` through ``RETURN`` sections are not used by the module code itself; they are essentially extra docstrings for the file. The imports are placed after these special variables for the same reason as PEP 8 puts the imports after the introductory comments and docstrings. This keeps the active parts of the code together and the pieces which are purely informational apart. The decision to exclude E402 is based on readability (which is what PEP 8 is about). Documentation strings in a module are much more similar to module level docstrings, than code, and are never utilized by the module itself. Placing the imports below this documentation and closer to the code, consolidates and groups all related code in a congruent manner to improve readability, debugging and understanding.

.. warning:: **Copy old modules with care!**

  Some older modules in Ansible Core have ``imports`` at the bottom of the file, ``Copyright`` notices with the full GPL prefix, and/or ``ANSIBLE_METADATA`` fields in the wrong order. These are legacy files that need updating - do not copy them into new modules. Over time we're updating and correcting older modules. Please follow the guidelines on this page!

.. _shebang:

Python shebang
==============

Every Ansible module must begin with ``#!/usr/bin/python`` - this "shebang" allows ``ansible_python_interpreter`` to work.

.. _copyright:

Copyright and license
=====================

After the shebang, there should be a `copyright line <https://www.gnu.org/licenses/gpl-howto.en.html>`_ with the original copyright holder and a license declaration. The license declaration should be ONLY one line, not the full GPL prefix.:

.. code-block:: python

    #!/usr/bin/python

    # Copyright: (c) 2018, Terry Jones <terry.jones@example.org>
    # GNU General Public License v3.0+ (see COPYING or https://www.gnu.org/licenses/gpl-3.0.txt)

Major additions to the module (for instance, rewrites) may add additional copyright lines. Any legal review will include the source control history, so an exhaustive copyright header is not necessary. When adding a second copyright line for a significant feature or rewrite, add the newer line above the older one:

.. code-block:: python

    #!/usr/bin/python

    # Copyright: (c) 2017, [New Contributor(s)]
    # Copyright: (c) 2015, [Original Contributor(s)]
    # GNU General Public License v3.0+ (see COPYING or https://www.gnu.org/licenses/gpl-3.0.txt)

.. _ansible_metadata_block:

ANSIBLE_METADATA block
======================

After the shebang, the copyright, and the license, your module file should contain an ``ANSIBLE_METADATA`` section. This section provides information about the module for use by other tools. For new modules, the following block can be simply added into your module:

.. code-block:: python

   ANSIBLE_METADATA = {'metadata_version': '1.1',
                       'status': ['preview'],
                       'supported_by': 'community'}

.. warning::

   * ``metadata_version`` is the version of the ``ANSIBLE_METADATA`` schema, *not* the version of the module.
   * Promoting a module's ``status`` or ``supported_by`` status should only be done by members of the Ansible Core Team.

Ansible metadata fields
-----------------------

:metadata_version: An "X.Y" formatted string. X and Y are integers which
   define the metadata format version. Modules shipped with Ansible are
   tied to an Ansible release, so we will only ship with a single version
   of the metadata. We'll increment Y if we add fields or legal values
   to an existing field. We'll increment X if we remove fields or values
   or change the type or meaning of a field.
   Current metadata_version is "1.1"

:supported_by: Who supports the module.
   Default value is ``community``. For information on what the support level values entail, please see
   :ref:`Modules Support <modules_support>`. Values are:

   * core
   * network
   * certified
   * community
   * curated (*deprecated value - modules in this category should be core or
     certified instead*)

:status: List of strings describing how stable the module is likely to be. See also :ref:`module_lifecycle`.
   The default value is a single element list ["preview"]. The following strings are valid
   statuses and have the following meanings:

   :stableinterface: The module's parameters are stable. Every effort will be made not to remove parameters or change
      their meaning. **Not** a rating of the module's code quality.
   :preview: The module is in tech preview. It may be
      unstable, the parameters may change, or it may require libraries or
      web services that are themselves subject to incompatible changes.
   :deprecated: The module is deprecated and will be removed in a future release.
   :removed: The module is not present in the release. A stub is
      kept so that documentation can be built. The documentation helps
      users port from the removed module to new modules.

.. _documentation_block:

DOCUMENTATION block
===================

After the shebang, the copyright line, the license, and the ``ANSIBLE_METADATA`` section comes the ``DOCUMENTATION`` block. Ansible's online module documentation is generated from the ``DOCUMENTATION`` blocks in each module's source code. The ``DOCUMENTATION`` block must be valid YAML. You may find it easier to start writing your ``DOCUMENTATION`` string in an :ref:`editor with YAML syntax highlighting <other_tools_and_programs>` before you include it in your Python file. You can start by copying our `example documentation string <https://github.com/ansible/ansible/blob/devel/examples/DOCUMENTATION.yml>`_ into your module file and modifying it. If you run into syntax issues in your YAML, you can validate it on the `YAML Lint <http://www.yamllint.com/>`_ website.

Module documentation should briefly and accurately define what each module and option does, and how it works with others in the underlying system. Documentation should be written for broad audience--readable both by experts and non-experts.
    * Descriptions should always start with a capital letter and end with a full stop. Consistency always helps.
    * Verify that arguments in doc and module spec dict are identical.
    * For password / secret arguments no_log=True should be set.
    * If an optional parameter is sometimes required, reflect this fact in the documentation, e.g. "Required when C(state=present)."
    * If your module allows ``check_mode``, reflect this fact in the documentation.

Each documentation field is described below. Before committing your module documentation, please test it at the command line and as HTML:

* As long as your module file is :ref:`available locally <local_modules>`, you can use ``ansible-doc -t module my_module_name`` to view your module documentation at the command line. Any parsing errors will be obvious - you can view details by adding ``-vvv`` to the command.
* You should also :ref:`test the HTML output <testing_module_documentation>` of your module documentation.

Documentation fields
--------------------

All fields in the ``DOCUMENTATION`` block are lower-case. All fields are required unless specified otherwise:

:module:

  * The name of the module.
  * Must be the same as the filename, without the ``.py`` extension.

:short_description:

  * A short description which is displayed on the :ref:`all_modules` page and ``ansible-doc -l``.
  * The ``short_description`` is displayed by ``ansible-doc -l`` without any category grouping,
    so it needs enough detail to explain the module's purpose without the context of the directory structure in which it lives.
  * Unlike ``description:``, ``short_description`` should not have a trailing period/full stop.

:description:

  * A detailed description (generally two or more sentences).
  * Must be written in full sentences, i.e. with capital letters and periods/full stops.
  * Shouldn't mention the module name.

:version_added:

  * The version of Ansible when the module was added.
  * This is a string, and not a float, i.e. ``version_added: "2.1"``

:author:

  * Name of the module author in the form ``First Last (@GitHubID)``.
  * Use a multi-line list if there is more than one author.

:deprecated:

  * Marks modules that will be removed in future releases. See also :ref:`module_lifecycle`.

:options:

  * If the module has no options (for example, it's a ``_facts`` module), all you need is one line: ``options: {}``.
  * If your module has options (in other words, accepts arguments), each option should be documented thoroughly. For each module argument/option, include:

  :option-name:

    * Declarative operation (not CRUD), to focus on the final state, for example `online:`, rather than `is_online:`.
    * The name of the option should be consistent with the rest of the module, as well as other modules in the same category.

  :description:

    * Detailed explanation of what this option does. It should be written in full sentences.
    * Should not list the possible values (that's what ``choices:`` is for, though it should explain `what` the values do if they aren't obvious).
    * If an optional parameter is sometimes required this need to be reflected in the documentation, e.g. "Required when I(state=present)."
    * Mutually exclusive options must be documented as the final sentence on each of the options.

  :required:

    * Only needed if ``true``.
    * If missing, we assume the option is not required.

  :default:

    * If ``required`` is false/missing, ``default`` may be specified (assumed 'null' if missing).
    * Ensure that the default parameter in the docs matches the default parameter in the code.
    * The default option must not be listed as part of the description.
    * If the option is a boolean value, you can use any of the boolean values recognized by Ansible:
      (such as true/false or yes/no).  Choose the one that reads better in the context of the option.

  :choices:

    * List of option values.
    * Should be absent if empty.

  :type:

    * Specifies the data type that option accepts, must match the ``argspec``.
    * If an argument is ``type='bool'``, this field should be set to ``type: bool`` and no ``choices`` should be specified.

  :aliases:
    * List of optional name aliases.
    * Generally not needed.

  :version_added:

    * Only needed if this option was extended after initial Ansible release, i.e. this is greater than the top level `version_added` field.
    * This is a string, and not a float, i.e. ``version_added: "2.3"``.

  :suboptions:

    * If this option takes a dict, you can define it here.
    * See :ref:`azure_rm_securitygroup_module`, :ref:`os_ironic_node_module` for examples.

:requirements:

  * List of requirements (if applicable).
  * Include minimum versions.

:notes:

  * Details of any important information that doesn't fit in one of the above sections.
  * For example, whether ``check_mode`` is or is not supported.

:seealso:

  * A list of references to other modules, documentation or Internet resources
  * A reference can be one of the following formats:


    .. code-block:: yaml+jinja

        seealso::

        # Reference by module name
        - module: aci_tenant

        # Reference by module name, including description
        - module: aci_tenant
          description: ACI module to create tenants on a Cisco ACI fabric.

        # Reference by rST documentation anchor
        - ref: aci_guide
          description: Detailed information on how to manage your ACI infrastructure using Ansible.

        # Reference by Internet resource
        - name: APIC Management Information Model reference
          description: Complete reference of the APIC object model.
          link: https://developer.cisco.com/docs/apic-mim-ref/


Linking within module documentation
-----------------------------------

You can link from your module documentation to other module docs, other resources on docs.ansible.com, and resources elsewhere on the internet. The correct formats for these links are:

* ``L()`` for Links with a heading. For example: ``See L(IOS Platform Options guide, ../network/user_guide/platform_ios.html).``
* ``U()`` for URLs. For example: ``See U(https://www.ansible.com/products/tower) for an overview.``
* ``I()`` for option names. For example: ``Required if I(state=present).``
* ``C()`` for files and option values. For example: ``If not set the environment variable C(ACME_PASSWORD) will be used.``
* ``M()`` for module names. For example: ``See also M(win_copy) or M(win_template).``

.. note::

    - To refer a collection of modules, use ``C(..)``, e.g. ``Refer to the C(win_*) modules.``
    - Because it stands out better, using ``seealso`` is preferred for general references over the use of notes or adding links to the description.

Documentation fragments
-----------------------

If you're writing multiple related modules, they may share common documentation, such as authentication details or file mode settings. Rather than duplicate that information in each module's ``DOCUMENTATION`` block, you can save it once as a fragment and use it in each module's documentation. Shared documentation fragments are contained in a ``ModuleDocFragment`` class in `lib/ansible/utils/module_docs_fragments/ <https://github.com/ansible/ansible/tree/devel/lib/ansible/utils/module_docs_fragments>`_. To include a documentation fragment, add ``extends_documentation_fragment: FRAGMENT_NAME`` in your module's documentation.

For example, all AWS modules should include::

.. code-block:: yaml+jinja

    extends_documentation_fragment:
        - aws
        - ec2


You can find more examples by searching for ``extends_documentation_fragment`` under the Ansible source tree.

.. _examples_block:

EXAMPLES block
==============

After the shebang, the copyright line, the license, the ``ANSIBLE_METADATA`` section, and the ``DOCUMENTATION`` block comes the ``EXAMPLES`` block. Here you show users how your module works with real-world examples in multi-line plain-text YAML format. The best examples are ready for the user to copy and paste into a playbook. Review and update your examples with every change to your module.

Per playbook best practices, each example should include a ``name:`` line::

    EXAMPLES = '''
    - name: Ensure foo is installed
      modulename:
        name: foo
        state: present
    '''

If your module returns facts that are often needed, an example of how to use them can be helpful.

.. _return_block:

RETURN block
============

After the shebang, the copyright line, the license, the ``ANSIBLE_METADATA`` section, ``DOCUMENTATION`` and ``EXAMPLES`` blocks comes the ``RETURN`` block. This section documents the information the module returns for use by other modules.

If your module doesn't return anything (apart from the standard returns), this section of your module should read: ``RETURN = ''' # '''``
Otherwise, for each value returned, provide the following fields. All fields are required unless specified otherwise.

:return name:
  Name of the returned field.

  :description:
    Detailed description of what this value represents.
  :returned:
    When this value is returned, such as ``always``, or ``on success``.
  :type:
    Data type.
  :sample:
    One or more examples.
  :version_added:
    Only needed if this return was extended after initial Ansible release, i.e. this is greater than the top level `version_added` field.
    This is a string, and not a float, i.e. ``version_added: "2.3"``.
  :contains:
    Optional. To describe nested return values, set ``type: complex`` and repeat the elements above for each sub-field.

Here are two example ``RETURN`` sections, one with three simple fields and one with a complex nested field::

    RETURN = '''
    dest:
        description: destination file/path
        returned: success
        type: string
        sample: /path/to/file.txt
    src:
        description: source file used for the copy on the target machine
        returned: changed
        type: string
        sample: /home/httpd/.ansible/tmp/ansible-tmp-1423796390.97-147729857856000/source
    md5sum:
        description: md5 checksum of the file after running copy
        returned: when supported
        type: string
        sample: 2a5aeecc61dc98c4d780b14b330e3282
    '''

    RETURN = '''
    packages:
        description: Information about package requirements
        returned: On success
        type: complex
        contains:
            missing:
                description: Packages that are missing from the system
                returned: success
                type: list
                sample:
                    - libmysqlclient-dev
                    - libxml2-dev
            badversion:
                description: Packages that are installed but at bad versions.
                returned: success
                type: list
                sample:
                    - package: libxml2-dev
                      version: 2.9.4+dfsg1-2
                      constraint: ">= 3.0"
    '''

.. _python_imports:

Python imports
==============

After the shebang, the copyright line, the license, and the sections for ``ANSIBLE_METADATA``, ``DOCUMENTATION``, ``EXAMPLES``, and ``RETURN``, you can finally add the python imports. All modules must use Python imports in the form:

.. code-block:: python

   from module_utils.basic import AnsibleModule

The use of "wildcard" imports such as ``from module_utils.basic import *`` is no longer allowed.
