'Return the latest item\'s pubdate or updateddate. If no items
have either of these attributes this return the current UTC date/time.'

def latest_post_date(self):

    latest_date = None
    date_keys = ('updateddate', 'pubdate')
    for item in self.items:
        for date_key in date_keys:
            item_date = item.get(date_key)
            if item_date:
                if ((latest_date is None) or (item_date > latest_date)):
                    latest_date = item_date
    return (latest_date or datetime.datetime.utcnow().replace(tzinfo=utc))
