Remove 3.6 compatibility shims

- asyncio.all_tasks/current_task
- pytest-asyncio 0.17
- contextmanager.nullcontext

jupyterhub/utils.py

@@ -27,14 +27,26 @@ from tornado import gen, ioloop, web
 from tornado.httpclient import AsyncHTTPClient, HTTPError
 from tornado.log import app_log
 
-# For compatibility with python versions 3.6 or earlier.
-# asyncio.Task.all_tasks() is fully moved to asyncio.all_tasks() starting with 3.9. Also applies to current_task.
-try:
-    asyncio_all_tasks = asyncio.all_tasks
-    asyncio_current_task = asyncio.current_task
-except AttributeError as e:
-    asyncio_all_tasks = asyncio.Task.all_tasks
-    asyncio_current_task = asyncio.Task.current_task
+
+# Deprecated aliases: no longer needed now that we require 3.7
+def asyncio_all_tasks(loop=None):
+    warnings.warn(
+        "jupyterhub.utils.asyncio_all_tasks is deprecated in JupyterHub 2.4."
+        " Use asyncio.all_tasks().",
+        DeprecationWarning,
+        stacklevel=2,
+    )
+    return asyncio.all_tasks(loop=loop)
+
+
+def asyncio_current_task(loop=None):
+    warnings.warn(
+        "jupyterhub.utils.asyncio_current_task is deprecated in JupyterHub 2.4."
+        " Use asyncio.current_task().",
+        DeprecationWarning,
+        stacklevel=2,
+    )
+    return asyncio.current_task(loop=loop)
 
 
 def random_port():