code: def opref(self):
      if not self._opref:
          encoded = self._read_opref()
          if encoded:
              try:
                  self._opref = opreflib.OpRef.parse(encoded)
              except opreflib.OpRefError as e:
                  raise opreflib.OpRefError(
                      f"invalid opref for run {self.id!r} ({self.path}): {e}"
                  )
      return self._opref
  
imports: import os
  import random
  import threading
  import time
  import uuid
  import yaml
  from guild import opref
  from guild import util
  from guild import yaml_util
label_desc: Use image node_id 4 for calling the Run obj's underlying member method code with example usage: obj.opref() and returns: self