code: def devno_free(self, devno):
          
          devno_int = int(devno, 16)
          self._devno_pool.free(devno_int)
docs: Free a device number allocated with :meth:`devno_alloc`.
  
          The device number must be allocated.
  
          Parameters:
            devno (string): The device number as four hexadecimal digits.
  
          Raises:
            ValueError: Device number not in pool range or not currently
              allocated.