diff --git a/dygraph/ptb_lm/ptb_dy.py b/dygraph/ptb_lm/ptb_dy.py
index 086901d7d5efb8a773551cdeaacb29829d966e80..48ff9bb7bdc3c210c8586bc744e10307c52a3b27 100644
--- a/dygraph/ptb_lm/ptb_dy.py
+++ b/dygraph/ptb_lm/ptb_dy.py
@@ -37,20 +37,25 @@ if sys.version[0] == '2':
     reload(sys)
     sys.setdefaultencoding("utf-8")
 
+
 class TimeCostAverage(object):
     def __init__(self):
         self.reset()
+
     def reset(self):
         self.cnt = 0
         self.total_time = 0
+
     def record(self, usetime):
         self.cnt += 1
         self.total_time += usetime
+
     def get_average(self):
         if self.cnt == 0:
             return 0
         return self.total_time / self.cnt
 
+
 class SimpleLSTMRNN(fluid.Layer):
     def __init__(self,
                  hidden_size,
@@ -454,7 +459,8 @@ def train_ptb_lm():
                         "-- Epoch:[%d]; Batch:[%d]; ppl: %.5f, lr: %.5f, loss: %.5f, batch_cost: %.5f s, reader_cost: %.5f s"
                         % (epoch_id, batch_id, ppl[0],
                            sgd._global_learning_rate().numpy(), out_loss,
-                           batch_cost_avg.get_average(), reader_cost_avg.get_average()))
+                           batch_cost_avg.get_average(),
+                           reader_cost_avg.get_average()))
                     batch_cost_avg.reset()
                     reader_cost_avg.reset()
                 batch_start = time.time()