Make floating-point exception error messages slightly more verbose: in

particular, the error message now allows one to distinguish between a
ValueError arising from a singularity (e.g. log(0.)), which would
usually produce +-infinity in non-stop mode, and a ValueError resulting
from an invalid input (e.g. sqrt(-1.)), which would normally produce a
NaN in non-stop mode.

Lib/test/ieee754.txt

@@ -127,31 +127,31 @@ Trigonometric Functions
 >>> sin(INF)
 Traceback (most recent call last):
 ...
-ValueError: math domain error
+ValueError: math domain error (invalid argument)
 >>> sin(NINF)
 Traceback (most recent call last):
 ...
-ValueError: math domain error
+ValueError: math domain error (invalid argument)
 >>> sin(NAN)
 nan
 >>> cos(INF)
 Traceback (most recent call last):
 ...
-ValueError: math domain error
+ValueError: math domain error (invalid argument)
 >>> cos(NINF)
 Traceback (most recent call last):
 ...
-ValueError: math domain error
+ValueError: math domain error (invalid argument)
 >>> cos(NAN)
 nan
 >>> tan(INF)
 Traceback (most recent call last):
 ...
-ValueError: math domain error
+ValueError: math domain error (invalid argument)
 >>> tan(NINF)
 Traceback (most recent call last):
 ...
-ValueError: math domain error
+ValueError: math domain error (invalid argument)
 >>> tan(NAN)
 nan
 
@@ -169,11 +169,11 @@ True
 >>> asin(INF), asin(NINF)
 Traceback (most recent call last):
 ...
-ValueError: math domain error
+ValueError: math domain error (invalid argument)
 >>> acos(INF), acos(NINF)
 Traceback (most recent call last):
 ...
-ValueError: math domain error
+ValueError: math domain error (invalid argument)
 >>> equal(atan(INF), PI/2), equal(atan(NINF), -PI/2)
 (True, True)
 

Lib/test/test_math.py

@@ -741,9 +741,9 @@ class MathTests(unittest.TestCase):
             func = getattr(math, fn)
             try:
                 result = func(ar)
-            except ValueError:
-                message = ("Unexpected ValueError in " +
-                           "test %s:%s(%r)\n" % (id, fn, ar))
+            except ValueError as exc:
+                message = (("Unexpected ValueError: %s\n        " +
+                           "in test %s:%s(%r)\n") % (exc.args[0], id, fn, ar))
                 self.fail(message)
             self.ftest("%s:%s(%r)" % (id, fn, ar), result, er)
 

Modules/mathmodule.c

@@ -174,18 +174,21 @@ math_1_to_whatever(PyObject *arg, double (*func) (double),
 	PyFPE_START_PROTECT("in math_1", return 0);
 	r = (*func)(x);
 	PyFPE_END_PROTECT(r);
-	if (Py_IS_NAN(r)) {
-		if (!Py_IS_NAN(x))
-			errno = EDOM;
-		else
-			errno = 0;
+	if (Py_IS_NAN(r) && !Py_IS_NAN(x)) {
+		PyErr_SetString(PyExc_ValueError,
+				"math domain error (invalid argument)");
+		return NULL;
 	}
-	else if (Py_IS_INFINITY(r)) {
-		if (Py_IS_FINITE(x))
-			errno = can_overflow ? ERANGE : EDOM;
+	if (Py_IS_INFINITY(r) && Py_IS_FINITE(x)) {
+			if (can_overflow)
+				PyErr_SetString(PyExc_OverflowError,
+					"math range error (overflow)");
 			else
-			errno = 0;
+				PyErr_SetString(PyExc_ValueError,
+					"math domain error (singularity)");
+			return NULL;
 	}
+	/* on most machines, errno should be 0 at this point */
 	if (errno && is_error(r))
 		return NULL;
 	else