iterator over artist's songs as :class:`Song` objects

def songs(self):
        """
        iterator over artist's songs as :class:`Song` objects
        """
        if self._songs is None:
            self._songs = [Song.from_response(song, self._connection) for song in
                           self._connection.request(
                               'artistGetArtistSongs',
                               {'artistID': self.id},
                               self._connection.header('artistGetArtistSongs'))[1]]
        return iter(self._songs)