class_docstr: NAS Tuner using Evolution Algorithm, with weight sharing enabled
code: def save_dir(self, indiv_id):
      if indiv_id is None:
          return None
      else:
          return os.path.join(self.save_dir_root, str(indiv_id))
  
imports: import copy
  import json
  import logging
  import random
  import os
  from threading import Event, Lock, current_thread
  from nni.tuner import Tuner
  from nni.utils import extract_scalar_reward
  from graph import Graph, Layer, LayerType, Enum, graph_dumps, graph_loads, unique
label_desc: Use image node_id 3 for calling the CustomerTuner obj's underlying member method code with example usage: obj.save_dir(indiv_id) and returns: None, os