code: def checkpoint_filename(checkpoint, pipeline_name=None):
      
      # Allow Stage as type for checkpoint parameter's argument without
      # needing to import here the Stage type from stage.py module.
      try:
          base = checkpoint.checkpoint_name
      except AttributeError:
          base = translate_stage_name(checkpoint)
      if pipeline_name:
          base = "{}{}{}".format(
              pipeline_name, PIPELINE_CHECKPOINT_DELIMITER, base)
      return base + CHECKPOINT_EXTENSION
docs: Translate a checkpoint to a filename.
  
      This not only adds the checkpoint file extension but also standardizes the
      way in which checkpoint names are mapped to filenames.
  
      :param str | pypiper.Stage checkpoint: name of a pipeline phase/stage
      :param str pipeline_name: name of pipeline to prepend to the checkpoint
          filename; this differentiates checkpoint files, e.g. within the
          same sample output folder but associated with different pipelines,
          in case of the (somewhat probable) scenario of a stage name
          collision between pipelines the processed the same sample and
          wrote to the same output folder
      :return str | NoneType: standardized checkpoint name for file, plus
          extension; null if the input is a Stage that's designated as a
          non-checkpoint