# documentação Django 2.0.8

# Código fonte para django.contrib.gis.feeds

    from django.contrib.syndication.views import Feed as BaseFeed
    from django.utils.feedgenerator import Atom1Feed, Rss201rev2Feed

    class GeoFeedMixin:
        """
        This mixin provides the necessary routines for SyndicationFeed subclasses
        to produce simple GeoRSS or W3C Geo elements.
        """

        def georss_coords(self, coords):
            """
            In GeoRSS coordinate pairs are ordered by lat/lon and separated by
            a single white space. Given a tuple of coordinates, return a string
            GeoRSS representation.
            """
            return ' '.join('%f %f' % (coord[1], coord[0]) for coord in coords)

        def add_georss_point(self, handler, coords, w3c_geo=False):
            """
            Adds a GeoRSS point with the given coords using the given handler.
            Handles the differences between simple GeoRSS and the more popular
            W3C Geo specification.
            """
            if w3c_geo:
                lon, lat = coords[:2]
                handler.addQuickElement('geo:lat', '%f' % lat)
                handler.addQuickElement('geo:lon', '%f' % lon)
            else:
                handler.addQuickElement('georss:point', self.georss_coords((coords,)))

        def add_georss_element(self, handler, item, w3c_geo=False):
            """Add a GeoRSS XML element using the given item and handler."""
            # Getting the Geometry object.
            geom = item.get('geometry')
            if geom is not None:
                if isinstance(geom, (list, tuple)):
                    # Special case if a tuple/list was passed in.  The tuple may be
                    # a point or a box
                    box_coords = None
                    if isinstance(geom[0], (list, tuple)):
                        # Box: ( (X0, Y0), (X1, Y1) )
                        if len(geom) == 2:
                            box_coords = geom
                        else:
                            raise ValueError('Only should be two sets of coordinates.')
                    else:
                        if len(geom) == 2:
                            # Point: (X, Y)
                            self.add_georss_point(handler, geom, w3c_geo=w3c_geo)
                        elif len(geom) == 4:
                            # Box: (X0, Y0, X1, Y1)
                            box_coords = (geom[:2], geom[2:])
                        else:
                            raise ValueError('Only should be 2 or 4 numeric elements.')
                    # If a GeoRSS box was given via tuple.
                    if box_coords is not None:
                        if w3c_geo:
                            raise ValueError('Cannot use simple GeoRSS box in W3C Geo feeds.')
                        handler.addQuickElement('georss:box', self.georss_coords(box_coords))
                else:
                    # Getting the lower-case geometry type.
                    gtype = str(geom.geom_type).lower()
                    if gtype == 'point':
                        self.add_georss_point(handler, geom.coords, w3c_geo=w3c_geo)
                    else:
                        if w3c_geo:
                            raise ValueError('W3C Geo only supports Point geometries.')
                        # For formatting consistent w/the GeoRSS simple standard:
                        # http://georss.org/1.0#simple
                        if gtype in ('linestring', 'linearring'):
                            handler.addQuickElement('georss:line', self.georss_coords(geom.coords))
                        elif gtype in ('polygon',):
                            # Only support the exterior ring.
                            handler.addQuickElement('georss:polygon', self.georss_coords(geom[0].coords))
                        else:
                            raise ValueError('Geometry type "%s" not supported.' % geom.geom_type)

    # ### SyndicationFeed subclasses ###
    class GeoRSSFeed(Rss201rev2Feed, GeoFeedMixin):
        def rss_attributes(self):
            attrs = super().rss_attributes()
            attrs['xmlns:georss'] = 'http://www.georss.org/georss'
            return attrs

        def add_item_elements(self, handler, item):
            super().add_item_elements(handler, item)
            self.add_georss_element(handler, item)

        def add_root_elements(self, handler):
            super().add_root_elements(handler)
            self.add_georss_element(handler, self.feed)

    class GeoAtom1Feed(Atom1Feed, GeoFeedMixin):
        def root_attributes(self):
            attrs = super().root_attributes()
            attrs['xmlns:georss'] = 'http://www.georss.org/georss'
            return attrs

        def add_item_elements(self, handler, item):
            super().add_item_elements(handler, item)
            self.add_georss_element(handler, item)

        def add_root_elements(self, handler):
            super().add_root_elements(handler)
            self.add_georss_element(handler, self.feed)

    class W3CGeoFeed(Rss201rev2Feed, GeoFeedMixin):
        def rss_attributes(self):
            attrs = super().rss_attributes()
            attrs['xmlns:geo'] = 'http://www.w3.org/2003/01/geo/wgs84_pos#'
            return attrs

        def add_item_elements(self, handler, item):
            super().add_item_elements(handler, item)
            self.add_georss_element(handler, item, w3c_geo=True)

        def add_root_elements(self, handler):
            super().add_root_elements(handler)
            self.add_georss_element(handler, self.feed, w3c_geo=True)

    # ### Feed subclass ###
    class Feed(BaseFeed):
        """
        This is a subclass of the `Feed` from `django.contrib.syndication`.
        This allows users to define a `geometry(obj)` and/or `item_geometry(item)`
        methods on their own subclasses so that geo-referenced information may
        placed in the feed.
        """
        feed_type = GeoRSSFeed

        def feed_extra_kwargs(self, obj):
            return {'geometry': self._get_dynamic_attr('geometry', obj)}

        def item_extra_kwargs(self, item):
            return {'geometry': self._get_dynamic_attr('item_geometry', item)}