fix-python-websockets#762: add asyncio_create_task as a compatability function

Author: DavidBord

src/websockets/compatibility.py

@@ -0,0 +1,6 @@
+import asyncio
+
+try:  # pragma: no cover
+    asyncio_create_task = asyncio.create_task  # Python ≥ 3.7
+except AttributeError:  # pragma: no cover
+    asyncio_create_task = asyncio.ensure_future  # Python < 3.7

src/websockets/server.py

@@ -28,6 +28,7 @@
     cast,
 )
 
+from .compatibility import asyncio_create_task
 from .exceptions import (
     AbortHandshake,
     InvalidHandshake,
@@ -715,9 +716,7 @@ async def _close(self) -> None:
         if self.websockets:
             await asyncio.wait(
                 [
-                    asyncio.ensure_future(websocket.close(1001))
-                    if sys.version_info[:2] < (3, 7)
-                    else asyncio.create_task(websocket.close(1001))
+                    asyncio_create_task(websocket.close(1001))
                     for websocket in self.websockets
                 ],
                 loop=self.loop if sys.version_info[:2] < (3, 8) else None,