PyGObject3 TreeModel

class CollectionModel(GObject.GObject, Gtk.TreeModel):
    NUM_COL = 4
    (ROWREF_ARTIST, ROWREF_ALBUM, ROWREF_DISC, ROWREF_SONG) = (1,2,3,4)
    COL_TYPES = (GObject.TYPE_STRING,
             GObject.TYPE_STRING,
             GObject.TYPE_STRING,
             GObject.TYPE_STRING)
    COL_NAMES = ("name",
             "file",
             "icon",
             "sort")
    # rowrefs are tuples with 2 elements:
    #   1 = type (Artist, Album, Disc, Song)
    #       2 = ID (if type is ROWREF_DISC, ID is a tuple of albumid and discid)
    def __init__(self, db):
        GObject.GObject.__init__(self)
        self.db = db

    def append(self, treeiter, data):
        # I don't need append()
        pass

    def do_get_column_names(self):
        return self.COL_NAMES[:]

    def do_get_flags(self):
        return 0

    def do_get_n_columns(self):
        return len(self.COL_TYPES)

    def do_get_column_type(self, n):
        return CollectionModel.COL_TYPES[n]

    def do_get_iter(self, path):
        path = path.get_indices()
        rowrefid = self.db.get_id_by_path(path)
        if not path or isinstance(path,int) or len(path) == 1:
            return (CollectionModel.ROWREF_ARTIST, rowrefid)
        elif len(path) == 2:
            return (CollectionModel.ROWREF_ALBUM, rowrefid)
        elif len(path) == 3:
            if isinstance(rowref,tuple):
                return (CollectionModel.ROWREF_DISC, rowrefid)
            else:
                return (CollectionModel.ROWREF_SONG, rowrefid)
        elif len(path) == 4:
            return (CollectionModel.ROWREF_SONG, rowrefid)
        return 0

    def do_get_path(self, rowref):
        if not rowref:
            return ()
        elif rowref[0] == CollectionModel.ROWREF_ARTIST:
            artistpos = self.db.get_artist_position_by_id(rowref[1])
            if artistpos:
                return (artistpos,)
        elif rowref[0] == CollectionModel.ROWREF_ALBUM:
            albumpos = self.db.get_albuetm_position_by_id(rowref[1])
            if albumpos:
                artistpos = self.db.get_artist_position_by_album_id(rowref[1])
                if artistpos:
                    return (artistpos, albumpos)
        elif rowref[0] == CollectionModel.ROWREF_DISC:
            discpos = (rowref[1][1]-1)
            if discpos:
                albumpos = self.db.get_album_position_by_id(rowref[1][1])
                if albumpos:
                    artistpos = self.db.get_artist_position_by_album_id(rowref[1])
                    if artistpos:
                        return (artistpos, albumpos, discpos)
        elif rowref[0] == CollectionModel.ROWREF_SONG:
            songpos = self.db.get_song_position_by_id(rowref[1])
            if songpos:
                discid = self.db.get_disc_by_song_id(rowref[1])
                albumpos = self.db.get_album_position_by_song_id(rowref[1])
                if albumpos:
                    artistpos = self.db.get_artist_song_by_id(rowref[1])
                    if artistpos:
                        if discid:
                            return (artistpos, albumpos, (discpos-1), songpos)
                        else:
                            return (artistpos, albumpos, songpos)
        return ()

    def do_get_value(self, rowref, column):
        print("do_get_value",rowref)
        if not rowref or not rowref:
            print("Damn it, something went wrong!")
            pass # This should NEVER happen
        elif rowref[0] == CollectionModel.ROWREF_ARTIST:
            if column == 0:
                return self.db.get_artist_name_by_id(rowref[1])
            elif column == 1:
                return ""
            elif column == 2:
                return str(Gtk.STOCK_ORIENTATION_PORTRAIT)
            elif column == 2:
                return ""
        elif rowref[0] == CollectionModel.ROWREF_ALBUM:
            if column == 0:
                return self.db.get_album_name_by_id(rowref[1])
            elif column == 1:
                return ""
            elif column == 2:
                return str(Gtk.STOCK_CDROM)
            elif column == 2:
                return ""
        elif rowref[0] == CollectionModel.ROWREF_DISC:
            if column == 0:
                return "CD %s" % str(rowref[1][1])
            elif column == 1:
                return ""
            elif column == 2:
                return ""
            elif column == 2:
                return ""
        elif rowref[0] == CollectionModel.ROWREF_SONG:
            if column == 0:
                return self.db.get_song_name_by_id(rowref[1])
            elif column == 1:
                return self.db.get_song_filename_by_id(rowref[1])
            elif column == 2:
                return ""
            elif column == 3:
                return ""

        raise InvalidColumnError(column)
        return "FUCK"

    def do_iter_next(self, rowref):
        if not rowref:
            return None
        return (rowref[0], self.db.get_next(rowref))

    def do_iter_children(self, rowref):
        """if not rowref or not rowref:
            return self.db.get_nth_artist(0)
        elif rowref[0] == CollectionModel.ROWREF_ARTIST:
            albumid = self.db.get_nth_album_by_artist_id(rowref[1])
            if albumid:
                return (CollectionModel.ROWREF_ALBUM, albumid)
        elif rowref[0] == CollectionModel.ROWREF_ALBUM:
            discid = self.db.get_nth_disc_by_album_id(rowref[1])
            if discid:
                return (CollectionModel.ROWREF_DISC, discid)
            else:
                songid = self.db.get_nth_song_by_album_id(rowref[1])
                if songid:
                    return (CollectionModel.ROWREF_SONG, songid)
        elif rowref[0] == CollectionModel.ROWREF_DISC:
            songid = self.db.get_nth_song_by_album_id(rowref[1][0], rowref[1][1])
            if songid:
                return (CollectionModel.ROWREF_SONG, songid)
        return None"""
        return self.do_iter_nth_child(self, rowref, 0)

    def do_iter_has_child(self, rowref):
        if not rowref:
            return True
        elif rowref[0] == CollectionModel.ROWREF_SONG:
            return False
        else:
            return True

    def do_iter_n_children(self, rowref):
        if not rowref:
            return self.db.get_artist_number()
        elif rowref[0] == CollectionModel.ROWREF_ARTIST:
            return self.db.get_album_number_by_artist_id(rowref[1])
        elif rowref[0] == CollectionModel.ROWREF_ALBUM:
            discnumber = self.db.get_disc_number_by_album_id(rowref[1])
            if discnumber:
                return discnumber
            else:
                return self.db.get_song_number_by_album_id(rowref[1])
        elif rowref[0] == CollectionModel.ROWREF_DISC:
            return self.db.get_song_number_by_album_id(rowref[1][0], rowref[1][1])
        return 0

    def do_iter_nth_child(self, rowref, n):
        if not rowref or not rowref:
            artistid = self.db.get_nth_artist(n)
            if artistid:
                return (CollectionModel.ROWREF_ARTIST, artistid)
        elif rowref[0] == CollectionModel.ROWREF_ARTIST:
            albumid = self.db.get_nth_album_by_artist_id(n, rowref[1])
            if albumid:
                return (CollectionModel.ROWREF_ALBUM, albumid)
        elif rowref[0] == CollectionModel.ROWREF_ALBUM:
            discid = self.db.get_nth_disc_by_album_id(n, rowref[1])
            if discid:
                return (CollectionModel.ROWREF_DISC, (albumid, discid))
            else:
                songid = self.db.get_nth_song_by_album_id(n, rowref[1])
                if songid:
                    return (CollectionModel.ROWREF_SONG, songid)
        elif rowref[0] == CollectionModel.ROWREF_DISC:
            songid = self.db.get_nth_song_by_album_id(n, rowref[1][0], rowref[1][1])
            if songid:
                return (CollectionModel.ROWREF_SONG, songid)
        return None

    def do_iter_parent(self, rowref):
        if not rowref:
            return None
        if rowref[0] == CollectionModel.ROWREF_SONG:
            albumid = self.db.get_album_by_song_id(rowref[1])
            discid = self.db.get_disc_by_song_id(rowref[1])
            if discid:
                return (CollectionModel.ROWREF_DISC, (albumid, discid))
            else:
                return (CollectionModel.ROWREF_ALBUM, albumid)
        elif rowref[0] == CollectionModel.ROWREF_ALBUM:
            return (CollectionModel.ROWREF_ARTIST, self.db.get_artist_by_album_id(rowref[1]))
        elif rowref[0] == CollectionModel.ROWREF_DISC:
            return (CollectionModel.ROWREF_ALBUM, rowref[1][0])
        return None