diff --git a/qlib/contrib/model/pytorch_lstm_ts.py b/qlib/contrib/model/pytorch_lstm_ts.py
index 70b8b0ce8..e703130fb 100755
--- a/qlib/contrib/model/pytorch_lstm_ts.py
+++ b/qlib/contrib/model/pytorch_lstm_ts.py
@@ -154,7 +154,7 @@ class LSTM(Model):
         mask = torch.isfinite(label)
 
         if self.metric in ("", "loss"):
-            return -self.loss_fn(pred[mask], label[mask], weight = None)
+            return -self.loss_fn(pred[mask], label[mask], weight=None)
 
         raise ValueError("unknown metric `%s`" % self.metric)