code: def _normalize_rename_handler(self, mapping, schema, field):
          
          if 'rename_handler' not in schema[field]:
              return
          new_name = self.__normalize_coerce(
              schema[field]['rename_handler'], field, field,
              False, errors.RENAMING_FAILED)
          if new_name != field:
              mapping[new_name] = mapping[field]
              del mapping[field]
docs: {'oneof': [
                  {'type': 'callable'},
                  {'type': 'list',
                   'schema': {'oneof': [{'type': 'callable'},
                                        {'type': 'string'}]}},
                  {'type': 'string'}
                  ]}