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Solve the following problem using Python, implementing the functions described below, one line at a time
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Description:
 def on(self):
 """Turn on the alsa_sink sink. This is done automatically when the sink is instantiated, so you'll only need to call this method if you ever call :meth:`off` and want to turn the sink back on. """

        assert spotifyconnect._session_instance.player.num_listeners(
            spotifyconnect.PlayerEvent.MUSIC_DELIVERY) == 0
        spotifyconnect._session_instance.player.on(
            spotifyconnect.PlayerEvent.MUSIC_DELIVERY, self._on_music_delivery)