MAINT: Return dicts from CheckpointManager.get_checkpoint.

The output is going to get converted to a dict anyway, and this makes it
easier to pipe output from a CheckpointManager directly to a
ContentsManager.

IPython/html/services/contents/filemanager.py

@@ -252,7 +252,7 b' class FileCheckpointManager(FileManagerMixin, CheckpointManager):'
     def get_checkpoint(self, checkpoint_id, path, type):
         """Get the content of a checkpoint.
 
-        Returns a pair of (content, type).
+        Returns a model suitable for passing to ContentsManager.save.
         """
         path = path.strip('/')
         self.log.info("restoring %s from checkpoint %s", path, checkpoint_id)
@@ -260,9 +260,20 b' class FileCheckpointManager(FileManagerMixin, CheckpointManager):'
         if not os.path.isfile(os_checkpoint_path):
             self.no_such_checkpoint(path, checkpoint_id)
         if type == 'notebook':
-            return self._read_notebook(os_checkpoint_path, as_version=4), None
+            return {
+                'type': type,
+                'content': self._read_notebook(
+                    os_checkpoint_path,
+                    as_version=4,
+                ),
+            }
         else:
-            return self._read_file(os_checkpoint_path, format=None)
+            content, format = self._read_file(os_checkpoint_path, format=None)
+            return {
+                'type': type,
+                'content': content,
+                'format': format,
+            }
 
     def rename_checkpoint(self, checkpoint_id, old_path, new_path):
         """Rename a checkpoint from old_path to new_path."""

IPython/html/services/contents/manager.py

@@ -523,19 +523,14 b' class ContentsManager(LoggingConfigurable):'
         """
         Restore a checkpoint.
         """
-        type = self.get(path, content=False)['type']
-        content, format = self.checkpoint_manager.get_checkpoint(
-            checkpoint_id,
-            path,
-            type,
+        return self.save(
+            model=self.checkpoint_manager.get_checkpoint(
+                checkpoint_id,
+                path,
+                self.get(path, content=False)['type']
+            ),
+            path=path,
         )
 
-        model = {
-            'type': type,
-            'content': content,
-            'format': format,
-        }
-        return self.save(model, path)
-
     def delete_checkpoint(self, checkpoint_id, path):
         return self.checkpoint_manager.delete_checkpoint(checkpoint_id, path)