diff --git a/dargs/notebook.py b/dargs/notebook.py
index 3904bda..bc3e89c 100644
--- a/dargs/notebook.py
+++ b/dargs/notebook.py
@@ -157,7 +157,11 @@ def __init__(self, data: dict, arg: Argument | Variant):
 
     def _init_subdata(self):
         """Initialize sub ArgumentData."""
-        if isinstance(self.data, dict) and isinstance(self.arg, Argument) and not self.arg.repeat:
+        if (
+            isinstance(self.data, dict)
+            and isinstance(self.arg, Argument)
+            and not self.arg.repeat
+        ):
             sub_fields = self.arg.sub_fields.copy()
             # extend subfiles with sub_variants
             for vv in self.arg.sub_variants.values():