I finally got the time to update and merge Mark's and my trunk-math branch. The patch is collaborated work of Mark Dickinson and me. It was mostly done a few months ago. The patch fixes a lot of loose ends and edge cases related to operations with NaN, INF, very small values and complex math.

The patch also adds acosh, asinh, atanh, log1p and copysign to all platforms. Finally it fixes differences between platforms like different results or exceptions for edge cases. Have fun :)

Lib/test/test_float.py

@@ -2,12 +2,12 @@
 import unittest, struct
 import os
 from test import test_support
+import math
+from math import isinf, isnan
+import operator
 
-def isinf(x):
-    return x * 0.5 == x
-
-def isnan(x):
-    return x != x
+INF = float("inf")
+NAN = float("nan")
 
 class FormatFunctionsTestCase(unittest.TestCase):
 
@@ -206,6 +206,17 @@ class InfNanTest(unittest.TestCase):
         self.assertEqual(str(1e300 * 1e300 * 0), "nan")
         self.assertEqual(str(-1e300 * 1e300 * 0), "nan")
 
+    def notest_float_nan(self):
+        self.assert_(NAN.is_nan())
+        self.failIf(INF.is_nan())
+        self.failIf((0.).is_nan())
+
+    def notest_float_inf(self):
+        self.assert_(INF.is_inf())
+        self.failIf(NAN.is_inf())
+        self.failIf((0.).is_inf())
+
+
 def test_main():
     test_support.run_unittest(
         FormatFunctionsTestCase,