How to use the feedgenerator.SyndicationFeed function in feedgenerator

"""
        updates = [i['pubdate'] for i in self.items if i['pubdate'] is not None]
        if len(updates) > 0:
            updates.sort()
            return updates[-1]
        else:
            return datetime.datetime.now()

class Enclosure(object):
    "Represents an RSS enclosure"
    def __init__(self, url, length, mime_type):
        "All args are expected to be Python Unicode objects"
        self.length, self.mime_type = length, mime_type
        self.url = iri_to_uri(url)

class RssFeed(SyndicationFeed):
    mime_type = 'application/rss+xml'
    def write(self, outfile, encoding):
        handler = SimplerXMLGenerator(outfile, encoding)
        handler.startDocument()
        handler.startElement("rss", self.rss_attributes())
        handler.startElement("channel", self.root_attributes())
        self.add_root_elements(handler)
        self.write_items(handler)
        self.endChannelElement(handler)
        handler.endElement("rss")

    def rss_attributes(self):
        return {"version": self._version,
                "xmlns:atom": "http://www.w3.org/2005/Atom"}

    def write_items(self, handler):

if item['unique_id'] is not None:
            handler.addQuickElement("guid", item['unique_id'])
        if item['ttl'] is not None:
            handler.addQuickElement("ttl", item['ttl'])

        # Enclosure.
        if item['enclosure'] is not None:
            handler.addQuickElement("enclosure", '',
                {"url": item['enclosure'].url, "length": item['enclosure'].length,
                    "type": item['enclosure'].mime_type})

        # Categories.
        for cat in item['categories']:
            handler.addQuickElement("category", cat)

class Atom1Feed(SyndicationFeed):
    # Spec: http://atompub.org/2005/07/11/draft-ietf-atompub-format-10.html
    mime_type = 'application/atom+xml'
    ns = "http://www.w3.org/2005/Atom"

    def write(self, outfile, encoding):
        handler = SimplerXMLGenerator(outfile, encoding)
        handler.startDocument()
        handler.startElement('feed', self.root_attributes())
        self.add_root_elements(handler)
        self.write_items(handler)
        handler.endElement("feed")

    def root_attributes(self):
        if self.feed['language'] is not None:
            return {"xmlns": self.ns, "xml:lang": self.feed['language']}
        else: