Literal use w/ python < 3.8 requires typing_extension, cach instead of check sys ver

Author: rwightman

timm/models/_hub.py

@@ -2,7 +2,6 @@
 import json
 import logging
 import os
-import sys
 from functools import partial
 from pathlib import Path
 from tempfile import TemporaryDirectory
@@ -22,9 +21,9 @@
 except ImportError:
     _has_safetensors = False
 
-if sys.version_info >= (3, 8):
+try:
     from typing import Literal
-else:
+except ImportError:
     from typing_extensions import Literal
 
 from timm import __version__

timm/models/vision_transformer.py

@@ -27,7 +27,11 @@
 import math
 from collections import OrderedDict
 from functools import partial
-from typing import Any, Callable, Dict, Optional, Sequence, Set, Tuple, Type, Union, Literal, List
+from typing import Any, Callable, Dict, Optional, Sequence, Set, Tuple, Type, Union, List
+try:
+    from typing import Literal
+except ImportError:
+    from typing_extensions import Literal
 
 import torch
 import torch.nn as nn