diff --git a/fastNLP/loader/dataset_loader.py b/fastNLP/loader/dataset_loader.py
index 91be0215..4ba121dd 100644
--- a/fastNLP/loader/dataset_loader.py
+++ b/fastNLP/loader/dataset_loader.py
@@ -87,7 +87,6 @@ class DataSetLoader(BaseLoader):
         """
         raise NotImplementedError
 
-
 @DataSet.set_reader('read_raw')
 class RawDataSetLoader(DataSetLoader):
     def __init__(self):
@@ -103,7 +102,6 @@ class RawDataSetLoader(DataSetLoader):
     def convert(self, data):
         return convert_seq_dataset(data)
 
-
 @DataSet.set_reader('read_pos')
 class POSDataSetLoader(DataSetLoader):
     """Dataset Loader for POS Tag datasets.
@@ -173,7 +171,6 @@ class POSDataSetLoader(DataSetLoader):
         """
         return convert_seq2seq_dataset(data)
 
-
 @DataSet.set_reader('read_tokenize')
 class TokenizeDataSetLoader(DataSetLoader):
     """
@@ -233,7 +230,6 @@ class TokenizeDataSetLoader(DataSetLoader):
     def convert(self, data):
         return convert_seq2seq_dataset(data)
 
-
 @DataSet.set_reader('read_class')
 class ClassDataSetLoader(DataSetLoader):
     """Loader for classification data sets"""
@@ -272,7 +268,6 @@ class ClassDataSetLoader(DataSetLoader):
     def convert(self, data):
         return convert_seq2tag_dataset(data)
 
-
 @DataSet.set_reader('read_conll')
 class ConllLoader(DataSetLoader):
     """loader for conll format files"""
@@ -314,7 +309,6 @@ class ConllLoader(DataSetLoader):
     def convert(self, data):
         pass
 
-
 @DataSet.set_reader('read_lm')
 class LMDataSetLoader(DataSetLoader):
     """Language Model Dataset Loader
@@ -351,7 +345,6 @@ class LMDataSetLoader(DataSetLoader):
     def convert(self, data):
         pass
 
-
 @DataSet.set_reader('read_people_daily')
 class PeopleDailyCorpusLoader(DataSetLoader):
     """