OVPNconsole/Django-1.0/docs/ref/contrib/syndication.txt

.. _ref-contrib-syndication:

==============================
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
========================

Overview
--------

The high-level feed-generating framework is a view that's hooked to ``/feeds/``
by default. Django uses the remainder of the URL (everything after ``/feeds/``)
to determine which feed to output.

To create a feed, just write a :class:`~django.contrib.syndication.feeds.Feed`
class and point to it in your :ref:`URLconf <topics-http-urls>`.

Initialization
--------------

If you're not using the latest Django development version, you'll need to make
sure Django's sites framework is installed -- including its database table. (See
the :mod:`sites framework documentation <django.contrib.sites>` for more
information.) This has changed in the Django development version; the
syndication feed framework no longer requires the sites framework.

To activate syndication feeds on your Django site, add this line to your
:ref:`URLconf <topics-http-urls>`::

   (r'^feeds/(?P<url>.*)/$', 'django.contrib.syndication.views.feed', {'feed_dict': feeds}),

This tells Django to use the RSS framework to handle all URLs starting with
:file:`"feeds/"`. (You can change that :file:`"feeds/"` prefix to fit your own
needs.)

This URLconf line has an extra argument: ``{'feed_dict': feeds}``. Use this
extra argument to pass the syndication framework the feeds that should be
published under that URL.

Specifically, :data:`feed_dict` should be a dictionary that maps a feed's slug
(short URL label) to its :class:`~django.contrib.syndication.feeds.Feed` class.

You can define the ``feed_dict`` in the URLconf itself. Here's a full example
URLconf::

    from django.conf.urls.defaults import *
    from myproject.feeds import LatestEntries, LatestEntriesByCategory

    feeds = {
        'latest': LatestEntries,
        'categories': LatestEntriesByCategory,
    }

    urlpatterns = patterns('',
        # ...
        (r'^feeds/(?P<url>.*)/$', 'django.contrib.syndication.views.feed',
            {'feed_dict': feeds}),
        # ...
    )

The above example registers two feeds:

    * The feed represented by ``LatestEntries`` will live at ``feeds/latest/``.
    * The feed represented by ``LatestEntriesByCategory`` will live at
      ``feeds/categories/``.

Once that's set up, you just need to define the
:class:`~django.contrib.syndication.feeds.Feed` classes themselves.

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

A :class:`~django.contrib.syndication.feeds.Feed` class is a simple 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).

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

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

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

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

    class LatestEntries(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]

Note:

* The class subclasses ``django.contrib.syndication.feeds.Feed``.

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

* :meth:`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
  :ref:`object-relational mapper <ref-models-querysets>`, :meth:`items()`
  doesn't have to return model instances. Although you get a few bits of
  functionality "for free" by using Django models, :meth:`items()` can
  return any type of object you want.

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

One thing's 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.

    * To specify the contents of ``<title>`` and ``<description>``, create
      :ref:`Django templates <topics-templates>` called
      :file:`feeds/latest_title.html`` and
      :file:`feeds/latest_description.html`, where :attr:`latest` is the
      :attr:`slug` specified in the URLconf for the given feed. Note the
      ``.html`` extension is required. The RSS system renders that template for
      each item, passing it two template context variables:

         * ``{{ obj }}`` -- The current object (one of whichever objects you
           returned in :meth:`items()`).
         
         * ``{{ site }}`` -- A :class:`django.contrib.sites.models.Site` object
           representing the current site. This is useful for ``{{ site.domain
           }}`` or ``{{ site.name }}``. Note that if you're using the latest
           Django development version and 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.

      If you don't create a template for either the title or description, the
      framework will use the template ``"{{ obj }}"`` by default -- that is, the
      normal string representation of the object. You can also change the names
      of these two templates by specifying ``title_template`` and
      ``description_template`` as attributes of your
      :class:`~django.contrib.syndication.feeds.Feed` class.

    * To specify the contents of ``<link>``, you have two options. For each item
      in :meth:`items()`, Django first tries executing a ``get_absolute_url()``
      method on that object. If that method doesn't exist, it tries calling a
      method :meth:`item_link()` in the
      :class:`~django.contrib.syndication.feeds.Feed` class, passing it a single
      parameter, :attr:`item`, which is the object itself. Both
      ``get_absolute_url()`` and :meth:`item_link()` should return the item's
      URL as a normal Python string. As with ``get_absolute_url()``, the result
      of :meth:`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.

    * For the LatestEntries example above, we could have very simple feed
      templates:

      * latest_title.html:

        .. code-block:: html+django

            {{ obj.title }}

      * latest_description.html:
      
        .. code-block:: html+django
      
            {{ obj.description }}

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

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

The framework also supports more complex feeds, via parameters.

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.feeds.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 make generic
feeds that output items based on information in the feed's URL.

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

    * :file:`/rss/beats/0613/` -- Returns recent crimes for beat 0613.
    * :file:`/rss/beats/1424/` -- Returns recent crimes for beat 1424.

The slug here is ``"beats"``. The syndication framework sees the extra URL bits
after the slug -- ``0613`` and ``1424`` -- and gives you a hook to tell it what
those URL bits mean, and how they should influence which items get published in
the feed.

An example makes this clear. Here's the code for these beat-specific feeds::

    from django.contrib.syndication.feeds import FeedDoesNotExist

    class BeatFeed(Feed):
        def get_object(self, bits):
            # In case of "/rss/beats/0613/foo/bar/baz/", or other such clutter,
            # check that bits has only one member.
            if len(bits) != 1:
                raise ObjectDoesNotExist
            return Beat.objects.get(beat__exact=bits[0])

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

        def link(self, obj):
            if not obj:
                raise FeedDoesNotExist
            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__id__exact=obj.id).order_by('-crime_date')[:30]

Here's the basic algorithm the RSS framework follows, given this class and a
request to the URL :file:`/rss/beats/0613/`:

    * The framework gets the URL :file:`/rss/beats/0613/` and notices there's an
      extra bit of URL after the slug. It splits that remaining string by the
      slash character (``"/"``) and calls the
      :class:`~django.contrib.syndication.feeds.Feed` class'
      :meth:`get_object()` method, passing it the bits. In this case, bits is
      ``['0613']``. For a request to :file:`/rss/beats/0613/foo/bar/`, bits
      would be ``['0613', 'foo', 'bar']``.

    * :meth:`get_object()` is responsible for retrieving the given beat, from
      the given ``bits``. In this case, it uses the Django database API to
      retrieve the beat. Note that :meth:`get_object()` should raise
      :exc:`django.core.exceptions.ObjectDoesNotExist` if given invalid
      parameters. There's no ``try``/``except`` around the
      ``Beat.objects.get()`` call, because it's not necessary; that function
      raises :exc:`Beat.DoesNotExist` on failure, and :exc:`Beat.DoesNotExist`
      is a subclass of :exc:`ObjectDoesNotExist`. Raising
      :exc:`ObjectDoesNotExist` in :meth:`get_object()` tells Django to produce
      a 404 error for that request.

      .. versionadded:: 1.0
         meth:`get_object()` can handle the :file:`/rss/beats/` url.

      The :meth:`get_object()` method also has a chance to handle the
      :file:`/rss/beats/` url. In this case, :data:`bits` will be an
      empty list. In our example, ``len(bits) != 1`` and an
      :exc:`ObjectDoesNotExist` exception will be raised, so
      :file:`/rss/beats/` will generate a 404 page. But you can handle this case
      however you like. For example, you could generate a combined feed for all
      beats.

    * To generate the feed's ``<title>``, ``<link>`` and ``<description>``,
      Django uses the :meth:`title()`, :meth:`link()` and :meth:`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 :attr:`title`, :attr:`link` and
      :attr:`description`, Django follows this algorithm:

        * First, it tries to call a method, passing the ``obj`` argument, where
          ``obj`` is the object returned by :meth:`get_object()`.
        
        * Failing that, it tries to call a method with no arguments.
        
        * Failing that, it uses the class attribute.

      Inside the :meth:`link()` method, we handle the possibility that ``obj``
      might be ``None``, which can occur when the URL isn't fully specified. In
      some cases, you might want to do something else in this case, which would
      mean you'd need to check for ``obj`` existing in other methods as well.
      (The :meth:`link()` method is called very early in the feed generation
      process, so it's a good place to bail out early.)

    * Finally, note that :meth:`items()` in this example also takes the ``obj``
      argument. The algorithm for :attr:`items` is the same as described in the
      previous step -- first, it tries :meth:`items(obj)`, then :meth:`items()`,
      then finally an :attr:`items` class attribute (which should be a list).

The ``ExampleFeed`` class below gives full documentation on methods and
attributes of :class:`~django.contrib.syndication.feeds.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.feeds.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
:attr:`item_enclosure_url`, :attr:`item_enclosure_length` and
:attr:`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 :attr:`link` method/attribute can return either an absolute URL (e.g.
:file:`"/blog/"`) or a URL with the fully-qualified domain and protocol (e.g.
``"http://www.example.com/blog/"``). If :attr:`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.feeds.Feed`
class and set the :attr:`feed_type` to something different. Then update your
URLconf to add the extra versions.

Here's a full example::

    from django.contrib.syndication.feeds 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 :attr:`description` while the Atom
    feed uses a :attr:`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 :attr:`description` in your
    :class:`~django.contrib.syndication.feeds.Feed` class, Django will *not*
    automatically put that into the :attr:`subtitle` element, because a
    subtitle and description are not necessarily the same thing. Instead, you
    should define a :attr:`subtitle` attribute.

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

And the accompanying URLconf::

    from django.conf.urls.defaults import *
    from myproject.feeds import RssSiteNewsFeed, AtomSiteNewsFeed

    feeds = {
        'rss': RssSiteNewsFeed,
        'atom': AtomSiteNewsFeed,
    }

    urlpatterns = patterns('',
        # ...
        (r'^feeds/(?P<url>.*)/$', 'django.contrib.syndication.views.feed',
            {'feed_dict': feeds}),
        # ...
    )

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

.. class:: django.contrib.syndication.feeds.Feed

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

    from django.contrib.syndication.feeds 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 you don't specify one, or either, Django will use the template
        # 'feeds/SLUG_title.html' and 'feeds/SLUG_description.html', where SLUG
        # is the slug you specify in the URL.

        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 e-mail as a normal Python string.
            """

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

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

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

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

        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, bits):
            """
            Takes a list of strings gleaned from the URL and returns an object
            represented by this feed. Raises
            django.core.exceptions.ObjectDoesNotExist on error.
            """

        # 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. This property is
        # only used for Atom feeds (it is the ID element for an item in an
        # Atom feed). 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 e-mail as a normal Python string.
            """

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

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

        # 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.

``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:

.. method:: SyndicationFeed.__init__(**kwargs)

    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.

.. method:: SyndicationFeed.add_item(**kwargs)

    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 datetime object`_.
        * ``enclosure`` should be an instance of ``feedgenerator.Enclosure``.
        * ``categories`` should be a sequence of Unicode objects.    

.. method:: SyndicationFeed.write(outfile, encoding)

    Outputs the feed in the given encoding to outfile, which is a file-like object.

.. method:: SyndicationFeed.writeString(encoding)

    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
    >>> 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")
    >>> f.add_item(title=u"Hot dog today",
    ...     link=u"http://www.example.com/entries/1/",
    ...     description=u"<p>Today I had a Vienna Beef hot dog. It was pink, plump and perfect.</p>")
    >>> print f.writeString('utf8')
    <?xml version="1.0" encoding="utf8"?>
    <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
.. _Python datetime object: http://www.python.org/doc/current/lib/module-datetime.html

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/store/podcaststechspecs.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 `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_attibutes(self):
            attrs = super(iTunesFeed, self).root_attibutes()
            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.

.. _XMLGenerator: http://docs.python.org/dev/library/xml.sax.utils.html#xml.sax.saxutils.XMLGenerator