code: def _ensure_output(self, run_id):
      if self._output_run_id == run_id:
          return
      run_dir = os.path.join(var.runs_dir(), run_id)
      if not os.path.exists(run_dir):
          raise NotFound()
      self._output = util.RunOutputReader(run_dir)
      self._output_run_id = run_id
  
imports: import json
  import logging
  import math
  import os
  import socket
  import subprocess
  import sys
  import threading
  import time
  from werkzeug.exceptions import NotFound
  from werkzeug.utils import redirect
  from guild import serving_util
  from guild import util
  from guild import var
label_desc: Use image node_id 3 for calling the RunOutput obj's underlying member method code with example usage: obj._ensure_output(run_id) without return types