code: def devno_alloc(self):
          
          devno_int = self._devno_pool.alloc()
          devno = "{:04X}".format(devno_int)
          return devno
docs: Allocates a device number unique to this partition, in the range of
          0x8000 to 0xFFFF.
  
          Returns:
            string: The device number as four hexadecimal digits in upper case.
  
          Raises:
            ValueError: No more device numbers available in that range.