diff --git a/km3io/tools.py b/km3io/tools.py
index 300da0e105b47c469e9d775aac68baca226fcb65..3bc0ee049b7399625b428e1e93730d23b89dfe5b 100644
--- a/km3io/tools.py
+++ b/km3io/tools.py
@@ -781,16 +781,18 @@ def is_CC(fobj):
     if all(len_w2lists <= 7):  # old nu file have w2list of len 7.
         usr = fobj.events.mc_tracks.usr_names
         cc_flag = usr[:, 0][:, 3]
-        out = (cc_flag == b'cc')  # not very reliable, found NC files with cc flag!
+        out = cc_flag == b"cc"  # not very reliable, found NC files with cc flag!
 
     else:
         if "gseagen" in program.lower():
             cc_flag = w2list[:, kw2gsg.W2LIST_GSEAGEN_CC]
-            out = (cc_flag > 0)
+            out = cc_flag > 0
         if "genhen" in program.lower():
             cc_flag = w2list[:, kw2gen.W2LIST_GENHEN_CC]
-            out = (cc_flag > 0)
+            out = cc_flag > 0
         else:
-            raise ValueError(f"simulation program {fobj.header.simul.program} is not implemented.")
+            raise ValueError(
+                f"simulation program {fobj.header.simul.program} is not implemented."
+            )
 
-    return out
\ No newline at end of file
+    return out
diff --git a/tests/test_tools.py b/tests/test_tools.py
index 7f325e7eb55f9e7716aa8fdf705d15ffa6d340cb..c79fe97b925bb3811f53b22b98546672adead76f 100644
--- a/tests/test_tools.py
+++ b/tests/test_tools.py
@@ -31,7 +31,9 @@ from km3io.tools import (
 )
 
 OFFLINE_FILE = OfflineReader(data_path("offline/km3net_offline.root"))
-GENHEN_OFFLINE_FILE = OfflineReader(data_path("offline/mcv5.1.genhen_anumuNC.sirene.jte.jchain.aashower.sample.root"))
+GENHEN_OFFLINE_FILE = OfflineReader(
+    data_path("offline/mcv5.1.genhen_anumuNC.sirene.jte.jchain.aashower.sample.root")
+)
 GSEAGEN_OFFLINE_FILE = OfflineReader(data_path("offline/numucc.root"))
 
 
@@ -528,6 +530,7 @@ class TestUnfoldIndices(unittest.TestCase):
         with self.assertRaises(IndexError):
             unfold_indices(data, indices)
 
+
 class TestIsCC(unittest.TestCase):
     def test_is_CC(self):
         NC_file = is_CC(GENHEN_OFFLINE_FILE)