Issue 1820: structseq objects did not work with the % formatting operator or isinstance(t, tuple).

Orignal patch (without tests) by Leif Walsh.

Lib/test/test_structseq.py

@@ -26,6 +26,12 @@ class StructSeqTest(unittest.TestCase):
         for i in xrange(-len(t), len(t)-1):
             self.assertEqual(t[i], astuple[i])
 
+    def test_tuple_subclass(self):
+        # Issue 1820
+        t = time.localtime()
+        s = ('%s ' * len(t)) % t        # This used to fail because t was not a tuple subclass
+        self.assert_(isinstance(t, tuple))
+
     def test_repr(self):
         t = time.gmtime()
         self.assert_(repr(t))