code: def device_id(self):
          
          if self.is_block:
              for filename in self._P.Block.Symlinks:
                  parts = decode_ay(filename).split('/')
                  if parts[-2] == 'by-id':
                      return parts[-1]
          elif self.is_drive:
              return self._assocdrive._P.Drive.Id
          return ''
docs: Return a unique and persistent identifier for the device.
  
          This is the basename (last path component) of the symlink in
          `/dev/disk/by-id/`.