Use with open() as fo: ... instead of try: fo = open(...) finally: fo.close()

fo is not set if the open() fails.

Lib/test/list_tests.py

@@ -57,13 +57,11 @@ class CommonTest(seq_tests.CommonTest):
         d.append(d)
         d.append(400)
         try:
-            fo = open(test_support.TESTFN, "wb")
+            with open(test_support.TESTFN, "wb") as fo:
                 print >> fo, d,
-            fo.close()
-            fo = open(test_support.TESTFN, "rb")
+            with open(test_support.TESTFN, "rb") as fo:
                 self.assertEqual(fo.read(), repr(d))
         finally:
-            fo.close()
             os.remove(test_support.TESTFN)
 
     def test_set_subscript(self):