This patch comes from upstream: http://bugs.python.org/issue21881

--- Python-2.7.8/Lib/test/test_tcl.py.~1~	2014-06-29 19:05:37.000000000 -0700

+++ Python-2.7.8/Lib/test/test_tcl.py	2014-07-17 20:50:53.804037105 -0700

@@ -420,10 +420,9 @@

             self.assertEqual(passValue(float('inf')), float('inf'))

             self.assertEqual(passValue(-float('inf')), -float('inf'))

         else:

-            f = float(passValue(float('nan')))

-            self.assertNotEqual(f, f)

             self.assertEqual(float(passValue(float('inf'))), float('inf'))

             self.assertEqual(float(passValue(-float('inf'))), -float('inf'))

+            # XXX NaN representation can be not parsable by float()

         self.assertEqual(passValue((1, '2', (3.4,))),

                          (1, '2', (3.4,)) if self.wantobjects else '1 2 3.4')

@@ -448,9 +447,6 @@

             expected = float(expected)

             self.assertAlmostEqual(float(actual), expected,

                                    delta=abs(expected) * 1e-10)

-        def nan_eq(actual, expected):

-            actual = float(actual)

-            self.assertNotEqual(actual, actual)

         check(True, '1')

         check(False, '0')

@@ -474,7 +470,7 @@

             check(f, f, eq=float_eq)

         check(float('inf'), 'Inf', eq=float_eq)

         check(-float('inf'), '-Inf', eq=float_eq)

-        check(float('nan'), 'NaN', eq=nan_eq)

+        # XXX NaN representation can be not parsable by float()

         check((), '')

         check((1, (2,), (3, 4), '5 6', ()), '1 2 {3 4} {5 6} {}')