code: def to_string(self):
      if self._as_string is None:
          self._as_string = self._components_to_string(
              job=self.job,
              replica=self.replica,
              task=self.task,
              device_type=self.device_type,
              device_index=self.device_index,
          )
      return self._as_string
  
imports: from tensorflow.python.util.tf_export import tf_export
  from tensorflow.python import pywrap_tfe
label_desc: Use image node_id 7 for calling the DeviceSpecV1 obj's underlying member method code with example usage: obj.to_string() and returns: self