Pass contextvars for Python3.7+ only

a2wsgi/wsgi.py

@@ -7,6 +7,12 @@
 
 from .types import Environ, Message, Receive, Scope, Send, StartResponse, WSGIApp
 
+try:
+    # Python 3.7+
+    import contextvars
+except ImportError:
+    contextvars = None
+
 
 class Body:
     def __init__(self, loop: asyncio.AbstractEventLoop, receive: Receive) -> None:
@@ -184,8 +190,11 @@ async def __call__(self, scope: Scope, receive: Receive, send: Send) -> None:
         sender = None
         try:
             sender = self.loop.create_task(self.sender(send))
-            context = contextvars.copy_context()
-            func = functools.partial(context.run, self.wsgi)
+            if contextvars is not None:
+                context = contextvars.copy_context()
+                func = functools.partial(context.run, self.wsgi)
+            else:
+                func = self.wsgi
             await self.loop.run_in_executor(
                 self.executor, func, environ, self.start_response
             )