code: def list_to_str(lst):
      s = ""
      for ele in lst:
          if s:
              s += " " + ele
          else:
              s = ele
      return s
  
imports: from typing import Optional
  from parlai.core.params import ParlaiParser
  from parlai.core.opt import Opt
  from parlai.core.teachers import FixedDialogTeacher
  from parlai.utils.io import PathManager
  from .build import build
  import json
  import os
label_desc: Use image node_id 2 for calling a global function with example usage: list_to_str(lst) and returns: s