Fix a potential NameError.
diff --git a/Lib/test/test_set.py b/Lib/test/test_set.py
index f263a7d..0e92551 100644
--- a/Lib/test/test_set.py
+++ b/Lib/test/test_set.py
@@ -297,8 +297,8 @@
         w = ReprWrapper()
         s = self.thetype([w])
         w.value = s
+        fo = open(support.TESTFN, "w")
         try:
-            fo = open(support.TESTFN, "w")
             fo.write(str(s))
             fo.close()
             fo = open(support.TESTFN, "r")