code: def variantcall_sample(data, region=None, align_bams=None, out_file=None):
      
      if out_file is None or not os.path.exists(out_file) or not os.path.lexists(out_file):
          utils.safe_makedir(os.path.dirname(out_file))
          ref_file = dd.get_ref_file(data)
          config = data["config"]
          caller_fns = get_variantcallers()
          caller_fn = caller_fns[config["algorithm"].get("variantcaller")]
          if len(align_bams) == 1:
              items = [data]
          else:
              items = multi.get_orig_items(data)
              assert len(items) == len(align_bams)
          assoc_files = tz.get_in(("genome_resources", "variation"), data, {})
          if not assoc_files: assoc_files = {}
          for bam_file in align_bams:
              bam.index(bam_file, data["config"], check_timestamp=False)
          out_file = caller_fn(align_bams, items, ref_file, assoc_files, region, out_file)
      if region:
          data["region"] = region
      data["vrn_file"] = out_file
      return [data]
docs: Parallel entry point for doing genotyping of a region of a sample.