diff --git a/km3io/offline.py b/km3io/offline.py
index 5d551666ad6e847f55515c2e035e53264321bf6d..c60a7a19e2be547033ca20edc177e8f5db884aad 100644
--- a/km3io/offline.py
+++ b/km3io/offline.py
@@ -11,6 +11,7 @@ BASKET_CACHE_SIZE = 110 * 1024**2
 
 class OfflineKeys:
     """wrapper for offline keys"""
+
     def __init__(self, file_path):
         """OfflineKeys is a class that reads all the available keys in an offline
         file and adapts the keys format to Python format.
@@ -273,6 +274,7 @@ class OfflineKeys:
 
 class Reader:
     """Reader for one offline ROOT file"""
+
     def __init__(self, file_path):
         """ Reader class is an offline ROOT file reader. This class is a
         "very" low level I/O.
@@ -340,6 +342,7 @@ class Reader:
 
 class OfflineReader:
     """reader for offline ROOT files"""
+
     def __init__(self, file_path, data=None):
         """ OfflineReader class is an offline ROOT file wrapper
 
@@ -756,6 +759,7 @@ class OfflineReader:
 
 class OfflineEvents:
     """wrapper for offline events"""
+
     def __init__(self, keys, values):
         """wrapper for offline events.
 
@@ -790,6 +794,7 @@ class OfflineEvents:
 
 class OfflineEvent:
     """wrapper for an offline event"""
+
     def __init__(self, keys, values):
         """wrapper for one offline event.
 
@@ -817,6 +822,7 @@ class OfflineEvent:
 
 class OfflineHits:
     """wrapper for offline hits"""
+
     def __init__(self, keys, values):
         """wrapper for offline hits.
 
@@ -851,6 +857,7 @@ class OfflineHits:
 
 class OfflineHit:
     """wrapper for an offline hit"""
+
     def __init__(self, keys, values):
         """wrapper for one offline hit.
 
@@ -887,6 +894,7 @@ class OfflineHit:
 
 class OfflineTracks:
     """wrapper for offline tracks"""
+
     def __init__(self, keys, values, fitparameters=None):
         """wrapper for offline tracks
 
@@ -931,6 +939,7 @@ class OfflineTracks:
 
 class OfflineTrack:
     """wrapper for an offline track"""
+
     def __init__(self, keys, values, fitparameters=None):
         """wrapper for one offline track.