code: def is_linguist_lookup(self, lookup):
          
          field = utils.get_field_name_from_lookup(lookup)
  
          # To keep default behavior with "FieldError: Cannot resolve keyword".
          if (
              field not in self.concrete_field_names
              and field in self.linguist_field_names
          ):
              return True
  
          return False
docs: Returns true if the given lookup is a valid linguist lookup.