diff --git a/znh5md/__init__.py b/znh5md/__init__.py
index d0afb65..6a26787 100644
--- a/znh5md/__init__.py
+++ b/znh5md/__init__.py
@@ -1,4 +1,5 @@
 """ZnH5MD: High Performance Interface for H5MD Trajectories."""
+
 import contextlib
 import importlib.metadata
 
diff --git a/znh5md/format/__init__.py b/znh5md/format/__init__.py
index 509bb6a..fba91bf 100644
--- a/znh5md/format/__init__.py
+++ b/znh5md/format/__init__.py
@@ -1,4 +1,5 @@
 """Format handler for h5md files."""
+
 import contextlib
 import dataclasses
 import typing
@@ -33,16 +34,14 @@ class GRP:
 
     @staticmethod
     def encode_boundary(value) -> np.ndarray:
-        return np.array(
-            [
-                (
-                    "periodic".encode(encoding="utf-8")
-                    if x
-                    else "none".encode(encoding="utf-8")
-                )
-                for x in value
-            ]
-        )
+        return np.array([
+            (
+                "periodic".encode(encoding="utf-8")
+                if x
+                else "none".encode(encoding="utf-8")
+            )
+            for x in value
+        ])
 
     @staticmethod
     def decode_boundary(value) -> np.ndarray: