diff --git a/xrft/tests/test_utils.py b/xrft/tests/test_utils.py
index 5767876..8485338 100644
--- a/xrft/tests/test_utils.py
+++ b/xrft/tests/test_utils.py
@@ -1,6 +1,7 @@
 """
 Test utility functions of xrft
 """
+
 import pytest
 import numpy as np
 import pandas as pd
diff --git a/xrft/utils.py b/xrft/utils.py
index c53b310..d47368d 100644
--- a/xrft/utils.py
+++ b/xrft/utils.py
@@ -1,6 +1,7 @@
 """
 Utility functions for xrft
 """
+
 import numpy as np
 
 from .xrft import _diff_coord
diff --git a/xrft/xrft.py b/xrft/xrft.py
index cec4740..fc498f1 100644
--- a/xrft/xrft.py
+++ b/xrft/xrft.py
@@ -209,7 +209,7 @@ def _diff_coord(coord):
         return np.diff(coord)
     elif pd.api.types.is_datetime64_dtype(v0):
         diff = np.diff(coord).astype("timedelta64[ns]").astype("f8")
-        diff = (diff/1e9) #convert back to seconds
+        diff = diff / 1e9  # convert back to seconds
         return diff
     else:
         return np.diff(coord)