code: def _path(opt, persona, use_cands):
      # Build the data if it doesn't exist.
      build(opt)
      datatype = opt["datatype"].split(":")[0]
      if datatype == "test":
          warn_once(
              "WARNING: Test set not included. Setting datatype to valid."
          )
          datatype = "valid"
      dt = datatype + "_" + persona
      cands = "" if use_cands else "_no_cands"
      return os.path.join(
          opt["datapath"], "ConvAI2", dt + cands + ".txt"
      )
  
imports: from parlai.core.teachers import FbDeprecatedDialogTeacher, YamlTeacher
  from parlai.utils.data import DatatypeHelper
  from parlai.utils.misc import warn_once
  from .build import build
  from parlai.utils.strings import normalize_reply
  import parlai.utils.logging
  from parlai.core.params import ParlaiParser
  from typing import Optional
  from parlai.core.opt import Opt
  import copy
  import os
label_desc: Use image node_id 1 for calling a global function with example usage: _path(opt, persona, use_cands) and returns: os