django/docs/ref/contrib/syndication.txt

==============================
The syndication feed framework
==============================

.. module:: django.contrib.syndication
   :synopsis: A framework for generating syndication feeds, in RSS and Atom,
              quite easily.

Django comes with a high-level syndication-feed-generating framework
that makes creating RSS_ and Atom_ feeds easy.

To create any syndication feed, all you have to do is write a short
Python class. You can create as many feeds as you want.

Django also comes with a lower-level feed-generating API. Use this if
you want to generate feeds outside of a Web context, or in some other
lower-level way.

.. _RSS: http://www.whatisrss.com/
.. _Atom: http://www.atomenabled.org/

The high-level framework
========================

.. versionchanged:: 1.2
   The high-level feeds framework was refactored in Django 1.2. The
   pre-1.2 interface still exists, but it has been deprecated, and
   will be removed in Django 1.4. If you need to maintain an old-style
   Django feed, please consult the Django 1.1 documentation. For
   details on updating to use the new high-level feed framework, see
   the :ref:`Django 1.2 release notes <1.2-updating-feeds>`.

Overview
--------

The high-level feed-generating framework is supplied by the
:class:`~django.contrib.syndication.views.Feed` class. To create a
feed, write a :class:`~django.contrib.syndication.views.Feed` class
and point to an instance of it in your :doc:`URLconf
</topics/http/urls>`.

Feed classes
------------

A :class:`~django.contrib.syndication.views.Feed` class is a Python
class that represents a syndication feed. A feed can be simple (e.g.,
a "site news" feed, or a basic feed displaying the latest entries of a
blog) or more complex (e.g., a feed displaying all the blog entries in
a particular category, where the category is variable).

Feed classes subclass :class:`django.contrib.syndication.views.Feed`.
They can live anywhere in your codebase.

Instances of :class:`~django.contrib.syndication.views.Feed` classes
are views which can be used in your :doc:`URLconf </topics/http/urls>`.

A simple example
----------------

This simple example, taken from `chicagocrime.org`_, describes a feed of the
latest five news items::

    from django.contrib.syndication.views import Feed
    from chicagocrime.models import NewsItem

    class LatestEntriesFeed(Feed):
        title = "Chicagocrime.org site news"
        link = "/sitenews/"
        description = "Updates on changes and additions to chicagocrime.org."

        def items(self):
            return NewsItem.objects.order_by('-pub_date')[:5]

        def item_title(self, item):
            return item.title

        def item_description(self, item):
            return item.description

To connect a URL to this feed, put an instance of the Feed object in
your :doc:`URLconf </topics/http/urls>`. For example::

    from django.conf.urls import patterns, url, include
    from myproject.feeds import LatestEntriesFeed

    urlpatterns = patterns('',
        # ...
        (r'^latest/feed/$', LatestEntriesFeed()),
        # ...
    )

Note:

* The Feed class subclasses :class:`django.contrib.syndication.views.Feed`.

* ``title``, ``link`` and ``description`` correspond to the
  standard RSS ``<title>``, ``<link>`` and ``<description>`` elements,
  respectively.

* ``items()`` is, simply, a method that returns a list of objects that
  should be included in the feed as ``<item>`` elements. Although this
  example returns ``NewsItem`` objects using Django's
  :doc:`object-relational mapper </ref/models/querysets>`, ``items()``
  doesn't have to return model instances. Although you get a few bits of
  functionality "for free" by using Django models, ``items()`` can
  return any type of object you want.

* If you're creating an Atom feed, rather than an RSS feed, set the
  ``subtitle`` attribute instead of the ``description`` attribute.
  See `Publishing Atom and RSS feeds in tandem`_, later, for an example.

One thing is left to do. In an RSS feed, each ``<item>`` has a ``<title>``,
``<link>`` and ``<description>``. We need to tell the framework what data to put
into those elements.

    * For the contents of ``<title>`` and ``<description>``, Django tries
      calling the methods ``item_title()`` and ``item_description()`` on
      the :class:`~django.contrib.syndication.views.Feed` class. They are passed
      a single parameter, ``item``, which is the object itself. These are
      optional; by default, the unicode representation of the object is used for
      both.

      If you want to do any special formatting for either the title or
      description, :doc:`Django templates </topics/templates>` can be used
      instead. Their paths can be specified with the ``title_template`` and
      ``description_template`` attributes on the
      :class:`~django.contrib.syndication.views.Feed` class. The templates are
      rendered for each item and are passed two template context variables:

         * ``{{ obj }}`` -- The current object (one of whichever objects you
           returned in ``items()``).

         * ``{{ site }}`` -- A :class:`django.contrib.sites.models.Site` object
           representing the current site. This is useful for ``{{ site.domain
           }}`` or ``{{ site.name }}``. If you do *not* have the Django sites
           framework installed, this will be set to a
           :class:`django.contrib.sites.models.RequestSite` object. See the
           :ref:`RequestSite section of the sites framework documentation
           <requestsite-objects>` for more.

      See `a complex example`_ below that uses a description template.

    * To specify the contents of ``<link>``, you have two options. For each item
      in ``items()``, Django first tries calling the
      ``item_link()`` method on the
      :class:`~django.contrib.syndication.views.Feed` class. In a similar way to
      the title and description, it is passed it a single parameter,
      ``item``. If that method doesn't exist, Django tries executing a
      ``get_absolute_url()`` method on that object. Both
      ``get_absolute_url()`` and ``item_link()`` should return the
      item's URL as a normal Python string. As with ``get_absolute_url()``, the
      result of ``item_link()`` will be included directly in the URL, so you
      are responsible for doing all necessary URL quoting and conversion to
      ASCII inside the method itself.

.. _chicagocrime.org: http://www.chicagocrime.org/

A complex example
-----------------

The framework also supports more complex feeds, via arguments.

For example, `chicagocrime.org`_ offers an RSS feed of recent crimes for every
police beat in Chicago. It'd be silly to create a separate
:class:`~django.contrib.syndication.views.Feed` class for each police beat; that
would violate the :ref:`DRY principle <dry>` and would couple data to
programming logic. Instead, the syndication framework lets you access the
arguments passed from your :doc:`URLconf </topics/http/urls>` so feeds can output
items based on information in the feed's URL.

On chicagocrime.org, the police-beat feeds are accessible via URLs like this:

    * :file:`/beats/613/rss/` -- Returns recent crimes for beat 613.
    * :file:`/beats/1424/rss/` -- Returns recent crimes for beat 1424.

These can be matched with a :doc:`URLconf </topics/http/urls>` line such as::

    (r'^beats/(?P<beat_id>\d+)/rss/$', BeatFeed()),

Like a view, the arguments in the URL are passed to the ``get_object()``
method along with the request object.

.. versionchanged:: 1.2
   Prior to version 1.2, ``get_object()`` only accepted a ``bits`` argument.

Here's the code for these beat-specific feeds::

    from django.contrib.syndication.views import FeedDoesNotExist
    from django.shortcuts import get_object_or_404

    class BeatFeed(Feed):
        description_template = 'feeds/beat_description.html'

        def get_object(self, request, beat_id):
            return get_object_or_404(Beat, pk=beat_id)

        def title(self, obj):
            return "Chicagocrime.org: Crimes for beat %s" % obj.beat

        def link(self, obj):
            return obj.get_absolute_url()

        def description(self, obj):
            return "Crimes recently reported in police beat %s" % obj.beat

        def items(self, obj):
            return Crime.objects.filter(beat=obj).order_by('-crime_date')[:30]

To generate the feed's ``<title>``, ``<link>`` and ``<description>``, Django
uses the ``title()``, ``link()`` and ``description()`` methods. In
the previous example, they were simple string class attributes, but this example
illustrates that they can be either strings *or* methods. For each of
``title``, ``link`` and ``description``, Django follows this
algorithm:

    * First, it tries to call a method, passing the ``obj`` argument, where
      ``obj`` is the object returned by ``get_object()``.

    * Failing that, it tries to call a method with no arguments.

    * Failing that, it uses the class attribute.

Also note that ``items()`` also follows the same algorithm -- first, it
tries ``items(obj)``, then ``items()``, then finally an ``items``
class attribute (which should be a list).

We are using a template for the item descriptions. It can be very simple:

.. code-block:: html+django

    {{ obj.description }}

However, you are free to add formatting as desired.

The ``ExampleFeed`` class below gives full documentation on methods and
attributes of :class:`~django.contrib.syndication.views.Feed` classes.

Specifying the type of feed
---------------------------

By default, feeds produced in this framework use RSS 2.0.

To change that, add a ``feed_type`` attribute to your
:class:`~django.contrib.syndication.views.Feed` class, like so::

    from django.utils.feedgenerator import Atom1Feed

    class MyFeed(Feed):
        feed_type = Atom1Feed

Note that you set ``feed_type`` to a class object, not an instance.

Currently available feed types are:

    * :class:`django.utils.feedgenerator.Rss201rev2Feed` (RSS 2.01. Default.)
    * :class:`django.utils.feedgenerator.RssUserland091Feed` (RSS 0.91.)
    * :class:`django.utils.feedgenerator.Atom1Feed` (Atom 1.0.)

Enclosures
----------

To specify enclosures, such as those used in creating podcast feeds, use the
``item_enclosure_url``, ``item_enclosure_length`` and
``item_enclosure_mime_type`` hooks. See the ``ExampleFeed`` class below for
usage examples.

Language
--------

Feeds created by the syndication framework automatically include the
appropriate ``<language>`` tag (RSS 2.0) or ``xml:lang`` attribute (Atom). This
comes directly from your :setting:`LANGUAGE_CODE` setting.

URLs
----

The ``link`` method/attribute can return either an absolute path (e.g.
:file:`"/blog/"`) or a URL with the fully-qualified domain and protocol (e.g.
``"http://www.example.com/blog/"``). If ``link`` doesn't return the domain,
the syndication framework will insert the domain of the current site, according
to your :setting:`SITE_ID setting <SITE_ID>`.

Atom feeds require a ``<link rel="self">`` that defines the feed's current
location. The syndication framework populates this automatically, using the
domain of the current site according to the :setting:`SITE_ID` setting.

Publishing Atom and RSS feeds in tandem
---------------------------------------

Some developers like to make available both Atom *and* RSS versions of their
feeds. That's easy to do with Django: Just create a subclass of your
:class:`~django.contrib.syndication.views.Feed`
class and set the ``feed_type`` to something different. Then update your
URLconf to add the extra versions.

Here's a full example::

    from django.contrib.syndication.views import Feed
    from chicagocrime.models import NewsItem
    from django.utils.feedgenerator import Atom1Feed

    class RssSiteNewsFeed(Feed):
        title = "Chicagocrime.org site news"
        link = "/sitenews/"
        description = "Updates on changes and additions to chicagocrime.org."

        def items(self):
            return NewsItem.objects.order_by('-pub_date')[:5]

    class AtomSiteNewsFeed(RssSiteNewsFeed):
        feed_type = Atom1Feed
        subtitle = RssSiteNewsFeed.description

.. Note::
    In this example, the RSS feed uses a ``description`` while the Atom
    feed uses a ``subtitle``. That's because Atom feeds don't provide for
    a feed-level "description," but they *do* provide for a "subtitle."

    If you provide a ``description`` in your
    :class:`~django.contrib.syndication.views.Feed` class, Django will *not*
    automatically put that into the ``subtitle`` element, because a
    subtitle and description are not necessarily the same thing. Instead, you
    should define a ``subtitle`` attribute.

    In the above example, we simply set the Atom feed's ``subtitle`` to the
    RSS feed's ``description``, because it's quite short already.

And the accompanying URLconf::

    from django.conf.urls import patterns, url, include
    from myproject.feeds import RssSiteNewsFeed, AtomSiteNewsFeed

    urlpatterns = patterns('',
        # ...
        (r'^sitenews/rss/$', RssSiteNewsFeed()),
        (r'^sitenews/atom/$', AtomSiteNewsFeed()),
        # ...
    )

Feed class reference
--------------------

.. class:: django.contrib.syndication.views.Feed

This example illustrates all possible attributes and methods for a
:class:`~django.contrib.syndication.views.Feed` class::

    from django.contrib.syndication.views import Feed
    from django.utils import feedgenerator

    class ExampleFeed(Feed):

        # FEED TYPE -- Optional. This should be a class that subclasses
        # django.utils.feedgenerator.SyndicationFeed. This designates
        # which type of feed this should be: RSS 2.0, Atom 1.0, etc. If
        # you don't specify feed_type, your feed will be RSS 2.0. This
        # should be a class, not an instance of the class.

        feed_type = feedgenerator.Rss201rev2Feed

        # TEMPLATE NAMES -- Optional. These should be strings
        # representing names of Django templates that the system should
        # use in rendering the title and description of your feed items.
        # Both are optional. If a template is not specified, the
        # item_title() or item_description() methods are used instead.

        title_template = None
        description_template = None

        # TITLE -- One of the following three is required. The framework
        # looks for them in this order.

        def title(self, obj):
            """
            Takes the object returned by get_object() and returns the
            feed's title as a normal Python string.
            """

        def title(self):
            """
            Returns the feed's title as a normal Python string.
            """

        title = 'foo' # Hard-coded title.

        # LINK -- One of the following three is required. The framework
        # looks for them in this order.

        def link(self, obj):
            """
            # Takes the object returned by get_object() and returns the feed's
            # link as a normal Python string.
            """

        def link(self):
            """
            Returns the feed's link as a normal Python string.
            """

        link = '/foo/bar/' # Hard-coded link.

        # GUID -- One of the following three is optional. The framework looks
        # for them in this order. This property is only used for Atom feeds
        # (where it is the feed-level ID element). If not provided, the feed
        # link is used as the ID.

        def feed_guid(self, obj):
            """
            Takes the object returned by get_object() and returns the globally
            unique ID for the feed as a normal Python string.
            """

        def feed_guid(self):
            """
            Returns the feed's globally unique ID as a normal Python string.
            """

        feed_guid = '/foo/bar/1234' # Hard-coded guid.

        # DESCRIPTION -- One of the following three is required. The framework
        # looks for them in this order.

        def description(self, obj):
            """
            Takes the object returned by get_object() and returns the feed's
            description as a normal Python string.
            """

        def description(self):
            """
            Returns the feed's description as a normal Python string.
            """

        description = 'Foo bar baz.' # Hard-coded description.

        # AUTHOR NAME --One of the following three is optional. The framework
        # looks for them in this order.

        def author_name(self, obj):
            """
            Takes the object returned by get_object() and returns the feed's
            author's name as a normal Python string.
            """

        def author_name(self):
            """
            Returns the feed's author's name as a normal Python string.
            """

        author_name = 'Sally Smith' # Hard-coded author name.

        # AUTHOR E-MAIL --One of the following three is optional. The framework
        # looks for them in this order.

        def author_email(self, obj):
            """
            Takes the object returned by get_object() and returns the feed's
            author's email as a normal Python string.
            """

        def author_email(self):
            """
            Returns the feed's author's email as a normal Python string.
            """

        author_email = 'test@example.com' # Hard-coded author email.

        # AUTHOR LINK --One of the following three is optional. The framework
        # looks for them in this order. In each case, the URL should include
        # the "http://" and domain name.

        def author_link(self, obj):
            """
            Takes the object returned by get_object() and returns the feed's
            author's URL as a normal Python string.
            """

        def author_link(self):
            """
            Returns the feed's author's URL as a normal Python string.
            """

        author_link = 'http://www.example.com/' # Hard-coded author URL.

        # CATEGORIES -- One of the following three is optional. The framework
        # looks for them in this order. In each case, the method/attribute
        # should return an iterable object that returns strings.

        def categories(self, obj):
            """
            Takes the object returned by get_object() and returns the feed's
            categories as iterable over strings.
            """

        def categories(self):
            """
            Returns the feed's categories as iterable over strings.
            """

        categories = ("python", "django") # Hard-coded list of categories.

        # COPYRIGHT NOTICE -- One of the following three is optional. The
        # framework looks for them in this order.

        def feed_copyright(self, obj):
            """
            Takes the object returned by get_object() and returns the feed's
            copyright notice as a normal Python string.
            """

        def feed_copyright(self):
            """
            Returns the feed's copyright notice as a normal Python string.
            """

        feed_copyright = 'Copyright (c) 2007, Sally Smith' # Hard-coded copyright notice.

        # TTL -- One of the following three is optional. The framework looks
        # for them in this order. Ignored for Atom feeds.

        def ttl(self, obj):
            """
            Takes the object returned by get_object() and returns the feed's
            TTL (Time To Live) as a normal Python string.
            """

        def ttl(self):
            """
            Returns the feed's TTL as a normal Python string.
            """

        ttl = 600 # Hard-coded Time To Live.

        # ITEMS -- One of the following three is required. The framework looks
        # for them in this order.

        def items(self, obj):
            """
            Takes the object returned by get_object() and returns a list of
            items to publish in this feed.
            """

        def items(self):
            """
            Returns a list of items to publish in this feed.
            """

        items = ('Item 1', 'Item 2') # Hard-coded items.

        # GET_OBJECT -- This is required for feeds that publish different data
        # for different URL parameters. (See "A complex example" above.)

        def get_object(self, request, *args, **kwargs):
            """
            Takes the current request and the arguments from the URL, and
            returns an object represented by this feed. Raises
            django.core.exceptions.ObjectDoesNotExist on error.
            """

        # ITEM TITLE AND DESCRIPTION -- If title_template or
        # description_template are not defined, these are used instead. Both are
        # optional, by default they will use the unicode representation of the
        # item.

        def item_title(self, item):
            """
            Takes an item, as returned by items(), and returns the item's
            title as a normal Python string.
            """

        def item_title(self):
            """
            Returns the title for every item in the feed.
            """

        item_title = 'Breaking News: Nothing Happening' # Hard-coded title.

        def item_description(self, item):
            """
            Takes an item, as returned by items(), and returns the item's
            description as a normal Python string.
            """

        def item_description(self):
            """
            Returns the description for every item in the feed.
            """

        item_description = 'A description of the item.' # Hard-coded description.

        # ITEM LINK -- One of these three is required. The framework looks for
        # them in this order.

        # First, the framework tries the two methods below, in
        # order. Failing that, it falls back to the get_absolute_url()
        # method on each item returned by items().

        def item_link(self, item):
            """
            Takes an item, as returned by items(), and returns the item's URL.
            """

        def item_link(self):
            """
            Returns the URL for every item in the feed.
            """

        # ITEM_GUID -- The following method is optional. If not provided, the
        # item's link is used by default.

        def item_guid(self, obj):
            """
            Takes an item, as return by items(), and returns the item's ID.
            """

        # ITEM AUTHOR NAME -- One of the following three is optional. The
        # framework looks for them in this order.

        def item_author_name(self, item):
            """
            Takes an item, as returned by items(), and returns the item's
            author's name as a normal Python string.
            """

        def item_author_name(self):
            """
            Returns the author name for every item in the feed.
            """

        item_author_name = 'Sally Smith' # Hard-coded author name.

        # ITEM AUTHOR E-MAIL --One of the following three is optional. The
        # framework looks for them in this order.
        #
        # If you specify this, you must specify item_author_name.

        def item_author_email(self, obj):
            """
            Takes an item, as returned by items(), and returns the item's
            author's email as a normal Python string.
            """

        def item_author_email(self):
            """
            Returns the author email for every item in the feed.
            """

        item_author_email = 'test@example.com' # Hard-coded author email.

        # ITEM AUTHOR LINK -- One of the following three is optional. The
        # framework looks for them in this order. In each case, the URL should
        # include the "http://" and domain name.
        #
        # If you specify this, you must specify item_author_name.

        def item_author_link(self, obj):
            """
            Takes an item, as returned by items(), and returns the item's
            author's URL as a normal Python string.
            """

        def item_author_link(self):
            """
            Returns the author URL for every item in the feed.
            """

        item_author_link = 'http://www.example.com/' # Hard-coded author URL.

        # ITEM ENCLOSURE URL -- One of these three is required if you're
        # publishing enclosures. The framework looks for them in this order.

        def item_enclosure_url(self, item):
            """
            Takes an item, as returned by items(), and returns the item's
            enclosure URL.
            """

        def item_enclosure_url(self):
            """
            Returns the enclosure URL for every item in the feed.
            """

        item_enclosure_url = "/foo/bar.mp3" # Hard-coded enclosure link.

        # ITEM ENCLOSURE LENGTH -- One of these three is required if you're
        # publishing enclosures. The framework looks for them in this order.
        # In each case, the returned value should be either an integer, or a
        # string representation of the integer, in bytes.

        def item_enclosure_length(self, item):
            """
            Takes an item, as returned by items(), and returns the item's
            enclosure length.
            """

        def item_enclosure_length(self):
            """
            Returns the enclosure length for every item in the feed.
            """

        item_enclosure_length = 32000 # Hard-coded enclosure length.

        # ITEM ENCLOSURE MIME TYPE -- One of these three is required if you're
        # publishing enclosures. The framework looks for them in this order.

        def item_enclosure_mime_type(self, item):
            """
            Takes an item, as returned by items(), and returns the item's
            enclosure MIME type.
            """

        def item_enclosure_mime_type(self):
            """
            Returns the enclosure MIME type for every item in the feed.
            """

        item_enclosure_mime_type = "audio/mpeg" # Hard-coded enclosure MIME type.

        # ITEM PUBDATE -- It's optional to use one of these three. This is a
        # hook that specifies how to get the pubdate for a given item.
        # In each case, the method/attribute should return a Python
        # datetime.datetime object.

        def item_pubdate(self, item):
            """
            Takes an item, as returned by items(), and returns the item's
            pubdate.
            """

        def item_pubdate(self):
            """
            Returns the pubdate for every item in the feed.
            """

        item_pubdate = datetime.datetime(2005, 5, 3) # Hard-coded pubdate.

        # ITEM CATEGORIES -- It's optional to use one of these three. This is
        # a hook that specifies how to get the list of categories for a given
        # item. In each case, the method/attribute should return an iterable
        # object that returns strings.

        def item_categories(self, item):
            """
            Takes an item, as returned by items(), and returns the item's
            categories.
            """

        def item_categories(self):
            """
            Returns the categories for every item in the feed.
            """

        item_categories = ("python", "django") # Hard-coded categories.

        # ITEM COPYRIGHT NOTICE (only applicable to Atom feeds) -- One of the
        # following three is optional. The framework looks for them in this
        # order.

        def item_copyright(self, obj):
            """
            Takes an item, as returned by items(), and returns the item's
            copyright notice as a normal Python string.
            """

        def item_copyright(self):
            """
            Returns the copyright notice for every item in the feed.
            """

        item_copyright = 'Copyright (c) 2007, Sally Smith' # Hard-coded copyright notice.


The low-level framework
=======================

Behind the scenes, the high-level RSS framework uses a lower-level framework
for generating feeds' XML. This framework lives in a single module:
`django/utils/feedgenerator.py`_.

You use this framework on your own, for lower-level feed generation. You can
also create custom feed generator subclasses for use with the ``feed_type``
``Feed`` option.

.. currentmodule:: django.utils.feedgenerator

``SyndicationFeed`` classes
---------------------------

The :mod:`~django.utils.feedgenerator` module contains a base class:

  * :class:`django.utils.feedgenerator.SyndicationFeed`

and several subclasses:

  * :class:`django.utils.feedgenerator.RssUserland091Feed`
  * :class:`django.utils.feedgenerator.Rss201rev2Feed`
  * :class:`django.utils.feedgenerator.Atom1Feed`

Each of these three classes knows how to render a certain type of feed as XML.
They share this interface:

:meth:`.SyndicationFeed.__init__`
    Initialize the feed with the given dictionary of metadata, which applies to
    the entire feed. Required keyword arguments are:

        * ``title``
        * ``link``
        * ``description``

    There's also a bunch of other optional keywords:

        * ``language``
        * ``author_email``
        * ``author_name``
        * ``author_link``
        * ``subtitle``
        * ``categories``
        * ``feed_url``
        * ``feed_copyright``
        * ``feed_guid``
        * ``ttl``

    Any extra keyword arguments you pass to ``__init__`` will be stored in
    ``self.feed`` for use with `custom feed generators`_.

    All parameters should be Unicode objects, except ``categories``, which
    should be a sequence of Unicode objects.

:meth:`.SyndicationFeed.add_item`
    Add an item to the feed with the given parameters.

    Required keyword arguments are:

        * ``title``
        * ``link``
        * ``description``

    Optional keyword arguments are:

        * ``author_email``
        * ``author_name``
        * ``author_link``
        * ``pubdate``
        * ``comments``
        * ``unique_id``
        * ``enclosure``
        * ``categories``
        * ``item_copyright``
        * ``ttl``

    Extra keyword arguments will be stored for `custom feed generators`_.

    All parameters, if given, should be Unicode objects, except:

        * ``pubdate`` should be a Python  :class:`~datetime.datetime` object.
        * ``enclosure`` should be an instance of
          :class:`django.utils.feedgenerator.Enclosure`.
        * ``categories`` should be a sequence of Unicode objects.

:meth:`.SyndicationFeed.write`
    Outputs the feed in the given encoding to outfile, which is a file-like object.

:meth:`.SyndicationFeed.writeString`
    Returns the feed as a string in the given encoding.

For example, to create an Atom 1.0 feed and print it to standard output::

    >>> from django.utils import feedgenerator
    >>> from datetime import datetime
    >>> f = feedgenerator.Atom1Feed(
    ...     title=u"My Weblog",
    ...     link=u"http://www.example.com/",
    ...     description=u"In which I write about what I ate today.",
    ...     language=u"en",
    ...     author_name=u"Myself",
    ...     feed_url=u"http://example.com/atom.xml")
    >>> f.add_item(title=u"Hot dog today",
    ...     link=u"http://www.example.com/entries/1/",
    ...     pubdate=datetime.now(),
    ...     description=u"<p>Today I had a Vienna Beef hot dog. It was pink, plump and perfect.</p>")
    >>> print f.writeString('UTF-8')
    <?xml version="1.0" encoding="UTF-8"?>
    <feed xmlns="http://www.w3.org/2005/Atom" xml:lang="en">
    ...
    </feed>

.. _django/utils/feedgenerator.py: http://code.djangoproject.com/browser/django/trunk/django/utils/feedgenerator.py

.. currentmodule:: django.contrib.syndication

Custom feed generators
----------------------

If you need to produce a custom feed format, you've got a couple of options.

If the feed format is totally custom, you'll want to subclass
``SyndicationFeed`` and completely replace the ``write()`` and
``writeString()`` methods.

However, if the feed format is a spin-off of RSS or Atom (i.e. GeoRSS_, Apple's
`iTunes podcast format`_, etc.), you've got a better choice. These types of
feeds typically add extra elements and/or attributes to the underlying format,
and there are a set of methods that ``SyndicationFeed`` calls to get these extra
attributes. Thus, you can subclass the appropriate feed generator class
(``Atom1Feed`` or ``Rss201rev2Feed``) and extend these callbacks. They are:

.. _georss: http://georss.org/
.. _itunes podcast format: http://www.apple.com/itunes/podcasts/specs.html

``SyndicationFeed.root_attributes(self, )``
    Return a ``dict`` of attributes to add to the root feed element
    (``feed``/``channel``).

``SyndicationFeed.add_root_elements(self, handler)``
    Callback to add elements inside the root feed element
    (``feed``/``channel``). ``handler`` is an
    :class:`~xml.sax.saxutils.XMLGenerator` from Python's built-in SAX library;
    you'll call methods on it to add to the XML document in process.

``SyndicationFeed.item_attributes(self, item)``
    Return a ``dict`` of attributes to add to each item (``item``/``entry``)
    element. The argument, ``item``, is a dictionary of all the data passed to
    ``SyndicationFeed.add_item()``.

``SyndicationFeed.add_item_elements(self, handler, item)``
    Callback to add elements to each item (``item``/``entry``) element.
    ``handler`` and ``item`` are as above.

.. warning::

    If you override any of these methods, be sure to call the superclass methods
    since they add the required elements for each feed format.

For example, you might start implementing an iTunes RSS feed generator like so::

    class iTunesFeed(Rss201rev2Feed):
        def root_attributes(self):
            attrs = super(iTunesFeed, self).root_attributes()
            attrs['xmlns:itunes'] = 'http://www.itunes.com/dtds/podcast-1.0.dtd'
            return attrs

        def add_root_elements(self, handler):
            super(iTunesFeed, self).add_root_elements(handler)
            handler.addQuickElement('itunes:explicit', 'clean')

Obviously there's a lot more work to be done for a complete custom feed class,
but the above example should demonstrate the basic idea.