code: def _dup_samples_by_variantcaller(samples, require_bam=True):
      
      samples = [utils.to_single_data(x) for x in samples]
      samples = germline.split_somatic(samples)
      to_process = []
      extras = []
      for data in samples:
          added = False
          for i, add in enumerate(handle_multiple_callers(data, "variantcaller", require_bam=require_bam)):
              added = True
              add = dd.set_variantcaller_order(add, i)
              to_process.append([add])
          if not added:
              data = _handle_precalled(data)
              data = dd.set_variantcaller_order(data, 0)
              extras.append([data])
      return to_process, extras
docs: Prepare samples by variant callers, duplicating any with multiple callers.