diff --git a/python/paddle/v2/plot_curve.py b/python/paddle/v2/plot_curve.py
index 9d24a87442b415f61de74d8f2444e06bf817c244..178506bbebdf3edaf78647e58178a2a6640cf9a1 100644
--- a/python/paddle/v2/plot_curve.py
+++ b/python/paddle/v2/plot_curve.py
@@ -6,6 +6,7 @@ class PlotCost(object):
     """
     append train and test cost in event_handle and then call plot.
     """
+
     def __init__(self):
         self.train_costs = ([], [])
         self.test_costs = ([], [])