diff --git a/dpdata/plugins/ase.py b/dpdata/plugins/ase.py
index 59022630e..3ee35c280 100644
--- a/dpdata/plugins/ase.py
+++ b/dpdata/plugins/ase.py
@@ -172,7 +172,7 @@ def to_system(self, data, **kwargs):
         return structures
 
     def to_labeled_system(self, data, *args, **kwargs):
-        """Convert System to ASE Atoms object. """
+        """Convert System to ASE Atoms object."""
         from ase import Atoms
         from ase.calculators.singlepoint import SinglePointCalculator