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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 _get_music_services_data_xml(soco=None):
 """Fetch the music services data xml from a Sonos device. Args: soco (SoCo):
 a SoCo instance to query. If none is specified, a random device will be used. Defaults to `None`. Returns: str: a string containing the music services data xml """

        device = soco or discovery.any_soco()
        log.debug("Fetching music services data from %s", device)
        available_services = device.musicServices.ListAvailableServices()
        descriptor_list_xml = available_services[
            'AvailableServiceDescriptorList']
        log.debug("Services descriptor list: %s", descriptor_list_xml)
        return descriptor_list_xml