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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 published_tracks(self):
 """ Access the published_tracks :returns: twilio.rest.video.v1.room.room_participant.room_participant_published_track.PublishedTrackList :rtype: twilio.rest.video.v1.room.room_participant.room_participant_published_track.PublishedTrackList """

        if self._published_tracks is None:
            self._published_tracks = PublishedTrackList(
                self._version,
                room_sid=self._solution['room_sid'],
                participant_sid=self._solution['sid'],
            )
        return self._published_tracks