code: def _get_unique_child(xtag, eltname):
      
      try:
          results = xtag.findall(eltname)
          if len(results) > 1:
              raise Exception("Multiple elements found where 0/1 expected")
          elif len(results) == 1:
              return results[0]
          else:
              return None
      except Exception:
          return None
docs: Get the unique child element under xtag with name eltname