diff --git a/src/dynamic_graph/__init__.py b/src/dynamic_graph/__init__.py
index c9a0924adb870e49b87d10fa78a4ceb022740382..7af1cfac8ca85e4c2a989865884c3d94d59cc35f 100644
--- a/src/dynamic_graph/__init__.py
+++ b/src/dynamic_graph/__init__.py
@@ -5,9 +5,6 @@ Author: Florent Lamiraux
 
 from __future__ import print_function
 
-import sys
-
 from . import entity  # noqa
 from . import signal_base  # noqa
-
 from .wrap import *  # noqa
diff --git a/src/dynamic_graph/entity.py b/src/dynamic_graph/entity.py
index 6374dc4e2be1221b51233c5cf2c8e63b4a32d718..9762042776b4c95193c7f34f91e6b0d2cf2bdda3 100644
--- a/src/dynamic_graph/entity.py
+++ b/src/dynamic_graph/entity.py
@@ -5,5 +5,5 @@
 from __future__ import print_function
 
 # for backward compat
-from .wrap import LoggerVerbosity as VerbosityLevel
-from .wrap import Entity
+from .wrap import LoggerVerbosity as VerbosityLevel  # noqa
+from .wrap import Entity  # noqa
diff --git a/src/dynamic_graph/signal_base.py b/src/dynamic_graph/signal_base.py
index ba40575e0fac4631d57c7d668fb6b060d20d0bc8..cfc065c7795a20ea37462eeed3635c273d5de0d4 100644
--- a/src/dynamic_graph/signal_base.py
+++ b/src/dynamic_graph/signal_base.py
@@ -4,12 +4,14 @@
 
 from __future__ import print_function
 
-from .wrap import SignalBase, create_signal_wrapper as SignalWrapper
-
 # I kept what follows for backward compatibility but I think it should be
 # removed
 import re
 
+from .wrap import SignalBase  # noqa
+from .wrap import create_signal_wrapper as SignalWrapper  # noqa
+
+
 def stringToTuple(vector):
     """
     Transform a string of format '[n](x_1,x_2,...,x_n)' into a tuple of numbers.