code: def _touch_checkpoint(self, check_file):
          
          if os.path.isabs(check_file):
              folder, _ = os.path.split(check_file)
              # For raw string comparison, ensure that each path
              # bears the final path separator.
              other_folder = os.path.join(folder, "")
              this_folder = os.path.join(self.outfolder, "")
              if other_folder != this_folder:
                  errmsg = "Path provided as checkpoint file isn't in pipeline " \
                           "output folder. '{}' is not in '{}'".format(
                          check_file, self.outfolder)
                  raise ValueError(errmsg)
              fpath = check_file
          else:
              fpath = pipeline_filepath(self, filename=check_file)
  
          # Create/update timestamp for checkpoint, but base return value on
          # whether the action was a simple update or a novel creation.
          already_exists = os.path.isfile(fpath)
          open(fpath, 'w').close()
          action = "Updated" if already_exists else "Created"
          print("{} checkpoint file: '{}'".format(action, fpath))
  
          return already_exists
docs: Alternative way for a pipeline to designate a checkpoint.
  
          :param str check_file: Name or path of file to use as checkpoint.
          :return bool: Whether a file was written (equivalent to whether the
              checkpoint file already existed).
          :raise ValueError: Raise a ValueError if the argument provided as the
              checkpoint file is an absolute path and that doesn't correspond
              to a location within the main output folder.