code: def _validate_indexer(self, form, key, kind):
          
          assert kind in ['ix', 'loc', 'getitem', 'iloc']
  
          if key is None:
              pass
          elif is_integer(key):
              pass
          elif kind in ['iloc', 'getitem']:
              self._invalid_indexer(form, key)
          return key
docs: If we are positional indexer, validate that we have appropriate
          typed bounds must be an integer.