Cap anyio < 3 for python < 3.7

jupyter_server/services/contents/filecheckpoints.py

@@ -14,7 +14,12 @@
 )
 from .fileio import AsyncFileManagerMixin, FileManagerMixin
 
-from anyio.to_thread import run_sync
+try:
+    from anyio.to_thread import run_sync
+except ImportError:
+    # fallback on anyio v2 for python version < 3.7
+    from anyio import run_sync_in_worker_thread as run_sync
+
 from jupyter_core.utils import ensure_dir_exists
 from traitlets import Unicode
 

jupyter_server/services/contents/fileio.py

@@ -12,7 +12,12 @@
 import os
 import shutil
 
-from anyio.to_thread import run_sync
+try:
+    from anyio.to_thread import run_sync
+except ImportError:
+    # fallback on anyio v2 for python version < 3.7
+    from anyio import run_sync_in_worker_thread as run_sync
+
 from tornado.web import HTTPError
 
 from jupyter_server.utils import (

jupyter_server/services/contents/filemanager.py

@@ -12,7 +12,12 @@
 import mimetypes
 import nbformat
 
-from anyio.to_thread import run_sync
+try:
+    from anyio.to_thread import run_sync
+except ImportError:
+    # fallback on anyio v2 for python version < 3.7
+    from anyio import run_sync_in_worker_thread as run_sync
+
 from send2trash import send2trash
 from tornado import web
 

jupyter_server/services/contents/largefilemanager.py

@@ -1,4 +1,9 @@
-from anyio.to_thread import run_sync
+try:
+    from anyio.to_thread import run_sync
+except ImportError:
+    # fallback on anyio v2 for python version < 3.7
+    from anyio import run_sync_in_worker_thread as run_sync
+
 from tornado import web
 import base64
 import os, io

setup.cfg

@@ -42,7 +42,8 @@ install_requires =
     terminado>=0.8.3
     prometheus_client
     pywin32>=1.0 ; sys_platform == 'win32'
-    anyio>=3.0.1,<4
+    anyio>=2.0.2,<3 ; python_version < '3.7'
+    anyio>=3.0.1,<4 ; python_version >= '3.7'
 
 [options.extras_require]
 test = coverage; pytest; pytest-cov; pytest-mock; requests; pytest-tornasync; pytest-console-scripts; ipykernel