code: def _init_taxids(taxid, taxids):
          
          ret = set()
          if taxids is not None:
              if taxids is True:
                  return True
              if isinstance(taxids, int):
                  ret.add(taxids)
              else:
                  ret.update(taxids)
          if taxid is not None:
              ret.add(taxid)
          if not ret:
              ret.add(9606)
              # pylint: disable=superfluous-parens
              print('**NOTE: DEFAULT TAXID STORED FROM gene2go IS 9606 (human)\n')
          return ret
docs: Return taxid set