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Solve the following problem using Python, implementing the functions described below, one line at a time
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<USER_TASK:>
Description:
 def _save_and_log_checkpoint(self, actor):
 """Save an actor checkpoint if necessary and log any errors. Args: actor: The actor to checkpoint. Returns: The result of the actor's user-defined `save_checkpoint` method. """

        actor_id = self._worker.actor_id
        checkpoint_info = self._worker.actor_checkpoint_info[actor_id]
        checkpoint_info.num_tasks_since_last_checkpoint += 1
        now = int(1000 * time.time())
        checkpoint_context = ray.actor.CheckpointContext(
            actor_id, checkpoint_info.num_tasks_since_last_checkpoint,
            now - checkpoint_info.last_checkpoint_timestamp)
        # If we should take a checkpoint, notify raylet to prepare a checkpoint
        # and then call `save_checkpoint`.
        if actor.should_checkpoint(checkpoint_context):
            try:
                now = int(1000 * time.time())
                checkpoint_id = (self._worker.raylet_client.
                                 prepare_actor_checkpoint(actor_id))
                checkpoint_info.checkpoint_ids.append(checkpoint_id)
                actor.save_checkpoint(actor_id, checkpoint_id)
                if (len(checkpoint_info.checkpoint_ids) >
                        ray._config.num_actor_checkpoints_to_keep()):
                    actor.checkpoint_expired(
                        actor_id,
                        checkpoint_info.checkpoint_ids.pop(0),
                    )
                checkpoint_info.num_tasks_since_last_checkpoint = 0
                checkpoint_info.last_checkpoint_timestamp = now
            except Exception:
                # Checkpoint save or reload failed. Notify the driver.
                traceback_str = ray.utils.format_error_message(
                    traceback.format_exc())
                ray.utils.push_error_to_driver(
                    self._worker,
                    ray_constants.CHECKPOINT_PUSH_ERROR,
                    traceback_str,
                    driver_id=self._worker.task_driver_id)