code: def ping(self):
      self._maybe_crash()
      return "pong"
  
imports: import functools
  import os
  from pathlib import Path
  import pickle
  import sys
  import time
  import unittest
  import ray
  from ray.util.state import list_actors
  from ray.rllib.utils.actor_manager import FaultAwareApply, FaultTolerantActorManager
label_desc: Use image node_id 4 for calling the Actor obj's underlying member method code with example usage: obj.ping() and returns: str