From ef9098a325eb7ed6d443a3241575754e8c559883 Mon Sep 17 00:00:00 2001
From: fengjiayi <fengjiayi@baidu.com>
Date: Wed, 24 Jan 2018 17:16:59 +0800
Subject: [PATCH] fix a bug

---
 python/paddle/v2/fluid/backward.py | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/python/paddle/v2/fluid/backward.py b/python/paddle/v2/fluid/backward.py
index ae81d68bafd..29243c90e87 100644
--- a/python/paddle/v2/fluid/backward.py
+++ b/python/paddle/v2/fluid/backward.py
@@ -178,7 +178,7 @@ def _remove_no_grad_branch_(op_descs, no_grad_set):
         if _all_in_set_(
                 filter(lambda name: name.find(core.grad_var_suffix()) != -1,
                        op_desc.input_arg_names()), no_grad_set):
-            no_grad_set.union(out_arg_names)
+            no_grad_set.update(out_arg_names)
             return True
         return False
 
-- 
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