code: def finish(self):
          
          # Update the last_offset in the mar header
          self.write_header()
          # Write out the index of contents
          self.write_index()
  
          if not self.use_old_format:
              # Refresh the signature
              sigs = self.calculate_signatures()
              self.write_signatures(sigs)
docs: Finalize the MAR file.
  
          The MAR header, index and signatures need to be updated once we've
          finished adding all the files.