code: def get_fields_by_class(cls, field_class):
          
  
          ret = []
  
          for key, val in getattr(cls, '_fields').items():
              if isinstance(val, field_class):
                  ret.append(key)
          return ret
docs: Return a list of field names matching a field class
  
          :param field_class: field class object
          :return: list