code: def stderr_file(self):
          
          stderr_file = None
          if self.connection_file is not None:
              stderr_file = self.kernel_id + '.stderr'
              if self.stderr_dir is not None:
                  stderr_file = osp.join(self.stderr_dir, stderr_file)
              else:
                  try:
                      stderr_file = osp.join(get_temp_dir(), stderr_file)
                  except (IOError, OSError):
                      stderr_file = None
          return stderr_file
docs: Filename to save kernel stderr output.