code: def compression_type(self):
          
          best_compression = None
          for e in self.mardata.index.entries:
              self.fileobj.seek(e.offset)
              magic = self.fileobj.read(10)
              compression = guess_compression(magic)
              if compression == 'xz':
                  best_compression = 'xz'
                  break
              elif compression == 'bz2' and best_compression is None:
                  best_compression = 'bz2'
          return best_compression
docs: Return the latest compresion type used in this MAR.
  
          Returns:
              One of None, 'bz2', or 'xz'