diff --git a/vcd/__init__.py b/vcd/__init__.py
index 5cc4ac4..8f0afbc 100644
--- a/vcd/__init__.py
+++ b/vcd/__init__.py
@@ -7,6 +7,7 @@
     ~vcd.reader.tokenize
 
 """
+
 from .reader import tokenize
 from .writer import VCDPhaseError, VCDWriter
 
diff --git a/vcd/gtkw.py b/vcd/gtkw.py
index 63098c7..3a7ef08 100644
--- a/vcd/gtkw.py
+++ b/vcd/gtkw.py
@@ -11,6 +11,7 @@
 __ http://gtkwave.sourceforge.net
 
 """
+
 import datetime
 import math
 import os
diff --git a/vcd/writer.py b/vcd/writer.py
index c530812..8957a90 100755
--- a/vcd/writer.py
+++ b/vcd/writer.py
@@ -3,6 +3,7 @@
 This module provides :class:`VCDWriter` for writing VCD files.
 
 """
+
 from datetime import datetime
 from itertools import zip_longest
 from numbers import Number