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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 device_id(self):
 """ Return a unique and persistent identifier for the device. This is the basename (last path component) of the symlink in `/dev/disk/by-id/`. """

        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 ''