Py 3.8 compatibility

src/whitenoise/asgi.py

@@ -25,8 +25,11 @@ async def __call__(self, scope, receive, send):
         # Determine if the request is for a static file
         static_file = None
         if scope["type"] == "http":
-            if self.autorefresh:
+            if self.autorefresh and hasattr(asyncio, "to_thread"):
+                # Use a thread while searching disk for files on Python 3.9+
                 static_file = await asyncio.to_thread(self.find_file, path)
+            elif self.autorefresh:
+                static_file = await self.find_file(path)
             else:
                 static_file = self.files.get(path)
 

src/whitenoise/middleware.py

@@ -152,8 +152,11 @@ def __init__(self, get_response=None, settings=settings):
             self.block_size = DEFAULT_BLOCK_SIZE
 
     async def __call__(self, request):
-        if self.autorefresh:
+        if self.autorefresh and hasattr(asyncio, "to_thread"):
+            # Use a thread while searching disk for files on Python 3.9+
             static_file = await asyncio.to_thread(self.find_file, request.path_info)
+        elif self.autorefresh:
+            static_file = self.find_file(request.path_info)
         else:
             static_file = self.files.get(request.path_info)
         if static_file is not None: