code: def _merge_outfile_fname(out_file, bam_files, work_dir, batch):
      
      if out_file is None:
          out_file = os.path.join(work_dir, os.path.basename(sorted(bam_files)[0]))
      if batch is not None:
          base, ext = os.path.splitext(out_file)
          out_file = "%s-b%s%s" % (base, batch, ext)
      return out_file
docs: Derive correct name of BAM file based on batching.