Allow to import from either jupyter_server or notebook packages

Ref. danielfrg#161

s3contents/ipycompat.py

@@ -19,9 +19,23 @@
     Checkpoints,
     GenericCheckpointsMixin,
 )
-from notebook.services.contents.filecheckpoints import GenericFileCheckpoints
-from notebook.services.contents.filemanager import FileContentsManager
-from notebook.services.contents.manager import ContentsManager
+
+# Ref. https://github.com/jupyter/nbdime/blob/c82362344e596efdc4f54c927d90338940e0fa41/nbdime/webapp/nb_server_extension.py#L16-L33
+# This allows solving conflicts between the class import from either notebook or jupyter_server
+try:
+    from notebook.services.contents.filecheckpoints import GenericFileCheckpoints
+    from notebook.services.contents.filemanager import FileContentsManager
+    from notebook.services.contents.manager import ContentsManager
+except ModuleNotFoundError:
+    pass
+
+try:
+    from jupyter_server.services.contents.filecheckpoints import GenericFileCheckpoints
+    from jupyter_server.services.contents.filemanager import FileContentsManager
+    from jupyter_server.services.contents.manager import ContentsManager
+except ModuleNotFoundError:
+    pass
+
 from notebook.utils import to_os_path
 from traitlets import (
     Any,