code: def get_root_directory(self, timestamp=None):
          
          if timestamp is None: timestamp = self.timestamp
          if self.timestamp_format is not None:
              root_name =  (time.strftime(self.timestamp_format, timestamp)
                            + '-' + self.batch_name)
          else:
              root_name = self.batch_name
  
          path = os.path.join(self.output_directory,
                                  *(self.subdir+[root_name]))
          return os.path.abspath(path)
docs: A helper method that supplies the root directory name given a
          timestamp.