diff -r 040eb15bbb6e Lib/decimal.py --- a/Lib/decimal.py Sun Aug 19 11:22:28 2012 +0200 +++ b/Lib/decimal.py Sun Aug 19 12:51:14 2012 +0100 @@ -1601,7 +1601,13 @@ def __float__(self): """Float representation.""" - return float(str(self)) + if self._isnan(): + if self.is_snan(): + raise ValueError("Cannot convert signaling NaN to float") + s = "-nan" if self._sign else "nan" + else: + s = str(self) + return float(s) def __int__(self): """Converts self to an int, truncating if necessary.""" diff -r 040eb15bbb6e Lib/test/test_decimal.py --- a/Lib/test/test_decimal.py Sun Aug 19 11:22:28 2012 +0200 +++ b/Lib/test/test_decimal.py Sun Aug 19 12:51:14 2012 +0100 @@ -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 diff -r 040eb15bbb6e Modules/_decimal/_decimal.c --- a/Modules/_decimal/_decimal.c Sun Aug 19 11:22:28 2012 +0200 +++ b/Modules/_decimal/_decimal.c Sun Aug 19 12:51:14 2012 +0100 @@ -3357,7 +3357,23 @@ { PyObject *f, *s; - s = dec_str(dec); + if (mpd_isnan(MPD(dec))) { + if (mpd_issnan(MPD(dec))) { + PyErr_SetString(PyExc_ValueError, + "cannot convert signaling NaN to float"); + return NULL; + } + if (mpd_isnegative(MPD(dec))) { + s = PyUnicode_FromString("-nan"); + } + else { + s = PyUnicode_FromString("nan"); + } + } + else { + s = dec_str(dec); + } + if (s == NULL) { return NULL; }