code: def _normalize_default_setter(self, mapping, schema, field):
          
          if 'default_setter' in schema[field]:
              setter = schema[field]['default_setter']
              if isinstance(setter, _str_type):
                  setter = self.__get_rule_handler('normalize_default_setter',
                                                   setter)
              mapping[field] = setter(mapping)
docs: {'oneof': [
                  {'type': 'callable'},
                  {'type': 'string'}
                  ]}