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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 id_to_extended_id(item_id, item_class):
 """Return the extended ID from an ID. :param item_id: The ID of the music library item :type item_id: str :param cls: The class of the music service item :type cls: Sub-class of :py:class:`soco.data_structures.MusicServiceItem` The extended id can be something like 00030020trackid_22757082 where the id is just trackid_22757082. For classes where the prefix is not known returns None. """

        out = ID_PREFIX[item_class]
        if out:
            out += item_id
        return out