diff --git a/bert_sklearn/config.py b/bert_sklearn/config.py
index eec63a5..36ea24e 100644
--- a/bert_sklearn/config.py
+++ b/bert_sklearn/config.py
@@ -99,9 +99,9 @@ def __init__(self, tokenizer=None, max_seq_length=64, train_sampler='random',
             self.ignore_label_id = np.array(self.ignore_label_id)
 
     def __repr__(self):
-        attrs = ["%s=%s"%(key, val) for key, val in vars(self).items()]
-        attrs = ",".join(attrs)
-        return f'{self.__class__.__name__}({attrs})'
+        attrs = ['{}={}'.format(key, val) for key, val in vars(self).items()]
+        attrs = ','.join(attrs)
+        return '{}({})'.format(self.__class__.__name__, attrs)
 
 
 def model2config(model):