# Epydoc Fields

Fields are used to describe specific properties of a documented object. For example, fields can be used to define the parameters and return value of a function; the instance variables of a class; and the author of a module. Each field consists of a tag, an optional argument, and a body.

- The tag is a case-insensitive word that indicates what kind of documentaiton is given by the field.
- The optional argument specifies what object, parameter, or group is documented by the field.
- The body contains the main contents of the field.

## 1. Field Markup

Each docstring markup langauge marks fields differently. The following table shows the basic fields syntax for each markup language. For more information, see the definition of field syntax for each markup language.

Epytext | reStructuredText | Javadoc
--- | --- | ---
`@tag: body`... `@tag arg: body`... | `:tag: body`... `:tag arg: body`... | `@tag body`... `@tag arg body`...
Definition of epytext fields | Definition of reStructuredText fields | Definition of Javadoc fields

## 2. Supported Fields

The following table lists the fields that epydoc currently recognizes. Field tags are written using epytext markup; if you are using a different markup language, then you should adjust the markup accordingly.

Functions and Methods (function or method docstrings)
`@param p:` ... | A description of the parameter `p` for a function or method. It may appear in the class docstring to describe a costructor parameter: mostly useful for C extensions.
`@type p:` ... | The expected type for the parameter. `p`.
`@return:` ... | The return value for a function or method.
`@rtype:` ... | The type of the return value for a function or method.
`@keyword p:` ... | A description of the keyword parameter `p`. It may appear in the class docstring to describe a costructor keyword parameter.
`@raise e:` ... | A description of the circumstances under which a function or method raises exception `e`. It may appear in the class docstring to describe an exception that can be raised by the costructor.
Variables (module, class or variable docstrings)
`@ivar v:` ... | A description of the class instance variable `v`.
`@cvar v:` ... | A description of the static class variable `v`.
`@var v:` ... | A description of the module variable `v`.
`@type v:` ... | The type of the variable `v`.
Properties (property docstrings)
`@type:` ... | The type of the property.
Grouping and Sorting (module, class, function, or method docstrings)
`@group g: c1,...,cn` | Organizes a set of related children of a module or class into a group. `g` is the name of the group; and `c1,...,cn` are the names of the children in the group. To define multiple groups, use multiple `group` fields.
`@sort: c1,...,cn` | Specifies the sort order for the children of a module or class. `c1,...,cn` are the names of the children, in the order in which they should appear. Any children that are not included in this list will appear after the children from this list, in alphabetical order.
Related Topics
`@see:` ... | A description of a related topic. `see` fields typically use documentation crossreference links or external hyperlinks that link to the related topic.
Notes and Warnings
`@note:` ... | A note about an object. Multiple `note` fields may be used to list separate notes.
`@attention:` ... | An important note about an object. Multiple `attention` fields may be used to list separate notes.
`@bug:` ... | A description of a bug in an object. Multiple `bug` fields may be used to report separate bugs.
`@warning:` ... | A warning about an object. Multiple `warning` fields may be used to report separate warnings.
Status
`@version:` ... | The current version of an object.
`@todo [ver]:` ... | A planned change to an object. If the optional argument `ver` is given, then it specifies the version for which the change will be made. Multiple `todo` fields may be used if multiple changes are planned.
`@deprecated:` ... | Indicates that an object is deprecated. The body of the field describe the reason why the object is deprecated.
`@since:` ... | The date or version when an object was first introduced.
`@status:` ... | The current status of an object.
`@change:` ... | A change log entry for this object.
`@permission:` ... | The object access permission, for systems such Zope/Plone supporting this concept. It may be used more than once to specify multiple permissions.
Formal Conditions
`@requires:` ... | A requirement for using an object. Multiple `requires` fields may be used if an object has multiple requirements.
`@precondition:` ... | A condition that must be true before an object is used. Multiple `precondition` fields may be used if an object has multiple preconditions.
`@postcondition:` ... | A condition that is guaranteed to be true after an object is used. Multiple `postcondition` fields may be used if an object has multiple postconditions.
`@invariant:` ... | A condition which should always be true for an object. Multiple `invariant` fields may be used if an object has multiple invariants.
Bibliographic Information
`@author:` ... | The author(s) of an object. Multiple `author` fields may be used if an object has multiple authors.
`@organization:` ... | The organization that created or maintains an object.
`@copyright:` ... | The copyright information for an object.
`@license:` ... | The licensing information for an object.
`@contact:` ... | Contact information for the author or maintainer of a module, class, function, or method. Multiple `contact` fields may be used if an object has multiple contacts.
Summarization
`@summary:` ... | A summary description for an object. This description overrides the default summary (which is constructed from the first sentence of the object's description).

### 2.1. Notes on Supported Fields

- `@param` fields should be used to document any explicit parameter (including the keyword parameter). `@keyword` fields should only be used for non-explicit keyword parameters:

      def plant(seed, *tools, **options):
          """
          @param seed: The seed that should be planted.
          @param tools: Tools that should be used to plant the seed.
          @param options: Any extra options for the planting.

          @keyword dig_deep: Plant the seed deep under ground.
          @keyword soak: Soak the seed before planting it.
          """
          [...]

- For the `@group` and `@sort` tags, asterisks (`*`) can be used to specify multiple children at once. An asterisk in a child name will match any substring:

      class widget(size, weight, age):
          """
          @group Tools: zip, zap, *_tool
          @group Accessors: get_*
          @sort: get_*, set_*, unpack_*, cut
          """
          [...]

- Since the `@type` field allows for arbitrary text, it does not automatically create a crossreference link to the specified type, and is not written in fixed-width font by default. If you want to create a crossreference link to the type, or to write the type in a fixed-width font, then you must use inline markup:

      def ponder(person, time):
          """
          @param person: Who should think.
          @type person: L{Person} or L{Animal}
          @param time: How long they should think.
          @type time: C{int} or C{float}
          """
          [...]

## 3. Where to Write Fields

Normally the fields are written in the docstring of the documented objects: this allows you to add fields to modules, classes, function, properties. Where a docstring is not allowed, usually alternative options do exist.

### 3.1. Variable docstrings

Python variables don't support docstrings. The variable can be described in the module or class where it is defined using the tags `@var`, `@ivar`, `@cvar`; but this only allows for a textual description: no further metadata can be added to the variable (except for the type, using the `@type` tag.

Epydoc supports variable docstrings: if a variable assignment statement is immediately followed by a bare string literal, then that assignment is treated as a docstring for that variable. In classes, variable assignments at the class definition level are considered class variables; and assignments to instance variables in the constructor (`__init__`) are considered instance variables:

    >>> class A:
    ...     x = 22
    ...     """Docstring for class variable A.x"""
    ...
    ...     def __init__(self, a):
    ...         self.y = a
    ...         """Docstring for instance variable A.y

Variables may also be documented using comment docstrings. If a variable assignment is immediately preceeded by a comment whose lines begin with the special marker "`#:`", or is followed on the same line by such a comment, then it is treated as a docstring for that variable:

    >>> #: docstring for x
    ... x = 22
    >>> x = 22 #: docstring for x

A common Python idiom is to create instance variables settings their default value in the class instead of the constructor (hopefully if the default is immutable...). To avoid Epydoc to interpret such variable as a class variable, you can describe it using the tag `@ivar` in the context of a variable docstring:

    >>> class B:
    ...     y = 42
    ...     """@ivar: This is an instance variable."""

Notice that variable docstrings are only available for documentation when the source code is available for parsing: it is not possible to retrieve variable docstrings from introspection informations only.

### 3.2. C Extensions

In a C extension module, extension classes cannot have a docstring attached to the `__init__` function; consequently it is not possible to document parameters and exceptions raised by the class constructor. To overcome this shortcoming, the tags `@param`, `@keyword`, `@type`, `@exception` are allowed to appear in the class docstring to refer to constructor parameters.

## 4. Field Synonyms

Several fields have "synonyms," or alternate tags. The following table lists all field synonyms. Field tags are written using epytext markup; if you are using a different markup language, then you should adjust the markup accordingly.

Name | Synonyms
--- | ---
`@param p:` ... | `@parameter p:` ... `@arg p:` ... `@argument p:` ...
`@return:` ... | `@returns:` ...
`@rtype:` ... | `@returntype:` ...
`@raise e:` ... | `@raises e:` ... `@except e:` ... `@exception e:` ...
`@keyword p:` ... | `@kwarg p:` ... `@kwparam p:` ...
`@ivar v:` ... | `@ivariable v:` ...
`@cvar v:` ... | `@cvariable v:` ...
Name | Synonyms
--- | ---
`@var v:` ... | `@variable v:` ...
`@see:` ... | `@seealso:` ...
`@warning:` ... | `@warn:` ...
`@requires:` ... | `@require:` ... `@requirement:` ...
`@precondition:` ... | `@precond:` ...
`@postcondition:` ... | `@postcod:` ...
`@organization:` ... | `@org:` ...
`@copyright:` ... | `@(c):` ...
`@change:` ... | `@changed:` ...

### 4.1. Metadata variables

Some module variables are commonly used as module metadata. Epydoc can use the value provided by these variables as alternate form for tags. The following table lists the recognized variables and the tag they replace. Customized metadata variables can be added using the method described in Adding New Fields.

Tag | Variable
--- | ---
`@deprecated` | `__deprecated__`
`@version` | `__version__`
`@date` | `__date__`
`@author` `@authors` | `__author__` `__authors__`
`@contact` | `__contact__`
`@copyright` | `__copyright__`
`@license` | `__license__`

## 5. Adding New Fields

New fields can be defined for the docstrings in a module using the special `@newfield` tag (or its synonym, `@deffield`). This tag has the following syntax:

    @newfield tag: label [, plural]

Where `tag` is the new tag that's being defined; `label` is a string that will be used to mark this field in the generated output; and `plural` is the plural form of `label`, if different.

It will also be possibile to use the module variable `__tag__` to set the value for the newly defined tag.

The following example illustrates how the `@newfield` can be used:

Docstring Input | Rendered Output
--- | ---
    """
    @newfield corpus: Corpus, Corpora
    """

    def example():
        """
        @corpus: Bob's wordlist.
        @corpus: The British National Corpus.
        """
        [...]
| Corpora: Bob's wordlist. The British National Corpus.

Note: The module-level variable `__extra_epydoc_fields__` is deprecated; use `@newfield` instead.

## 6. Markup-Specific Notes

For the most part, fields are treated identically, regardless of what markup language is used to encode them. However, there are a few minor differences, which are intended to accomodate existing standards for each markup language. In particular:

- reStructuredText supports an extra group of fields, called consolidated fields, which combine the documentation for several objects into a single field.
- Javadoc uses a special syntax for the body of the `@see` fields.
- Javadoc does not support multi-word arguments.

For more information about these differences, read the subsections below.

### 6.1. reStructuredText Fields

In reStructuredText, a single field can be used to encode the documentation for a group of related items. For example, a single `:Parameters:` field is often used to describe all of the parameters for a function or method:

    def fox_speed(size, weight, age):
        """
        Return the maximum speed for a fox.

        :Parameters:
          - `size`: The size of the fox (in meters)
          - `weight`: The weight of the fox (in stones)
          - `age`: The age of the fox (in years)
        """
        [...]

Epydoc will automatically extract information about each parameter from this list. These consolidated fields may be written using either a bulleted list or a definition list. If a consolidated field is written as a bulleted list, then each list item must begin with the field's argument, marked as interpreted text, and followed by a colon or dash. If a consolidated field is written as a definition list, then each definition item's term should contain the field's argument, (it is not mandatory for it being marked as interpreted text). The term classifier, if present, is used to specify the associated type. The following example shows the use of a definition list to define a consolidated field. (Note that docutils requires a space before and after the ":" used to mark classifiers.)

    def fox_speed(size, weight, age):
        """
        Return the maximum speed for a fox.

        :Parameters:
          size
              The size of the fox (in meters)
          weight : float
              The weight of the fox (in stones)
          age : int
              The age of the fox (in years)
        """
        [...]

The following consolidated fields are currently supported by epydoc:

Consolidated Field Tag | Corresponding Base Field Tag
--- | ---
`:Parameters:` | `:param:`
`:Exceptions:` | `:except:`
`:Groups:` | `:group:`
`:Keywords:` | `:keyword:`
Consolidated Field Tag | Corresponding Base Field Tag
--- | ---
`:Variables:` | `:var:`
`:Ivariables:` | `:ivar:`
`:Cvariables:` | `:cvar:`
`:Types:` | `:type:`

### 6.2. Javadoc Fields

For compatibility with Javadoc, every `@see` field is assumed to contain a single crossreference link, unless its body is quoted, or it starts with an HTML tag. See the Javadoc reference manual for more information about how the `@see` field is encoded in Javadoc.

Because Javadoc does not mark end of the optional argument, field arguments must contain exactly one word. Thus, multi-word arguments are not available in Javadoc. In particular, all group names must be single words.