code: def grid_file_path(self):
          
          if os.path.isfile(self.grid_xml_path):
              return self.grid_xml_path
          else:
              raise GridXmlFileNotFoundError
docs: Validate that grid file path points to a file.
  
          :return: The grid xml file path.
          :rtype: str
  
          :raises: GridXmlFileNotFoundError