diff -r 083534cd7874 Lib/decimal.py --- a/Lib/decimal.py Thu Aug 02 17:50:06 2012 -0400 +++ b/Lib/decimal.py Fri Aug 03 19:01:52 2012 +1000 @@ -1601,6 +1601,8 @@ def __float__(self): """Float representation.""" + if self.is_qnan(): + return _math.copysign(float('nan'), (-1)**self._sign) return float(str(self)) def __int__(self): diff -r 083534cd7874 Lib/test/test_decimal.py --- a/Lib/test/test_decimal.py Thu Aug 02 17:50:06 2012 -0400 +++ b/Lib/test/test_decimal.py Fri Aug 03 19:01:52 2012 +1000 @@ -1942,6 +1942,22 @@ for d, n, r in test_triples: self.assertEqual(str(round(Decimal(d), n)), r) + def test_nan_to_float(self): + # Test conversions of decimal NANs to float. + # See http://bugs.python.org/issue15544 + Decimal = self.decimal.Decimal + for s in ('nan', 'nan1234', '-nan', '-nan2468'): + f = float(Decimal(s)) + self.assertTrue(math.isnan(f)) + sign = math.copysign(1.0, f) + self.assertEqual(sign, -1.0 if s.startswith('-') else 1.0) + + def test_snan_to_float(self): + Decimal = self.decimal.Decimal + for s in ('snan', '-snan', 'snan1357', '-snan1234'): + d = Decimal(s) + self.assertRaises(ValueError, float, d) + def test_eval_round_trip(self): Decimal = self.decimal.Decimal