Update NATS-Bench (sss version 1.0)

lib/nats_bench/api_utils.py

@@ -10,10 +10,15 @@
 # History:
 # [2020.07.31] The first version, where most content reused nas_201_api/api_utils.py
 #
-import os, abc, copy, random, torch, numpy as np
-from pathlib import Path
+import abc, copy, random, numpy as np
+import importlib, warnings
 from typing import List, Text, Union, Dict, Optional
 from collections import OrderedDict, defaultdict
+USE_TORCH = importlib.find_loader('torch') is not None
+if USE_TORCH:
+  import torch
+else:
+  warnings.warn('Can not find PyTorch, and thus some features maybe invalid.')
 
 
 def remap_dataset_set_names(dataset, metric_on_set, verbose=False):
@@ -545,6 +550,8 @@ class ArchResults(object):
   def create_from_state_dict(state_dict_or_file):
     x = ArchResults(-1, -1)
     if isinstance(state_dict_or_file, str): # a file path
+      if not USE_TORCH:
+        raise ValueError('Since torch is not imported, this logic can not be used.')
       state_dict = torch.load(state_dict_or_file, map_location='cpu')
     elif isinstance(state_dict_or_file, dict):
       state_dict = state_dict_or_file