code: def parse(self, data, extent, desc_tag):
          # type: (bytes, int, UDFTag) -> None
          '''
          Parse the passed in data into a UDF Unallocated Space Descriptor.
  
          Parameters:
           data - The data to parse.
           extent - The extent that this descriptor currently lives at.
           desc_tag - A UDFTag object that represents the Descriptor Tag.
          Returns:
           Nothing.
          '''
          if self._initialized:
              raise pycdlibexception.PyCdlibInternalError('UDF Unallocated Space Descriptor already initialized')
  
          (tag_unused, self.vol_desc_seqnum,
           num_alloc_descriptors, end_unused) = struct.unpack_from(self.FMT, data, 0)
  
          self.desc_tag = desc_tag
  
          if num_alloc_descriptors != 0:
              raise pycdlibexception.PyCdlibInvalidISO('UDF Unallocated Space Descriptor allocated descriptors is not 0')
  
          self.orig_extent_loc = extent
  
          self._initialized = Truf parse(self, data, extent, desc_tag):
          # type: (bytes, int, UDFTag) -> None
          '''
          Parse the passed in data into a UDF Unallocated Space Descriptor.
  
          Parameters:
           data - The data to parse.
           extent - The extent that this descriptor currently lives at.
           desc_tag - A UDFTag object that represents the Descriptor Tag.
          Returns:
           Nothing.
          '''
          if self._initialized:
              raise pycdlibexception.PyCdlibInternalError('UDF Unallocated Space Descriptor already initialized')
  
          (tag_unused, self.vol_desc_seqnum,
           num_alloc_descriptors, end_unused) = struct.unpack_from(self.FMT, data, 0)
  
          self.desc_tag = desc_tag
  
          if num_alloc_descriptors != 0:
              raise pycdlibexception.PyCdlibInvalidISO('UDF Unallocated Space Descriptor allocated descriptors is not 0')
  
          self.orig_extent_loc = extent
  
          self._initialized = True
docs: Parse the passed in data into a UDF Unallocated Space Descriptor.
  
          Parameters:
           data - The data to parse.
           extent - The extent that this descriptor currently lives at.
           desc_tag - A UDFTag object that represents the Descriptor Tag.
          Returns:
           Nothing.