Add tests for math.atan2() and update NEWS

Author: hpkfft

Lib/test/test_math.py

@@ -348,6 +348,15 @@ def testAtan2(self):
         self.assertTrue(math.isnan(math.atan2(NAN, 2.3)))
         self.assertTrue(math.isnan(math.atan2(NAN, INF)))
         self.assertTrue(math.isnan(math.atan2(NAN, NAN)))
+        # overflow and underflow of y/x
+        self.assertEqual(math.atan2(1E-320, 1E300), 0.0)
+        self.assertEqual(math.atan2(-1E-320, 1E300), -0.0)
+        self.assertAlmostEqual(math.atan2(1E300, 1E-320), math.pi/2)
+        self.assertAlmostEqual(math.atan2(1E300, -1E-320), math.pi/2)
+        self.assertAlmostEqual(math.atan2(1E-320, -1E300), math.pi)
+        self.assertAlmostEqual(math.atan2(-1E-320, -1E300), -math.pi)
+        self.assertAlmostEqual(math.atan2(-1E300, 1E-320), -math.pi/2)
+        self.assertAlmostEqual(math.atan2(-1E300, -1E-320), -math.pi/2)
 
     def testCbrt(self):
         self.assertRaises(TypeError, math.cbrt)

Misc/NEWS.d/next/Library/2026-07-20-09-35-32.gh-issue-153144.0a2AoO.rst

@@ -1,3 +1,4 @@
-The function :func:`cmath.phase` should not raise ``OverflowError``, and the
-functions :func:`math.atan2`, :func:`math.atan2pi`, and :func:`cmath.phase`
-should not raise ``ValueError``.  Contributed by High Performance Kernels LLC.
+:func:`math.atan2` and :func:`math.atan2pi` no longer raise :exc:`ValueError`.
+:func:`cmath.phase` no longer raises :exc:`OverflowError` or :exc:`ValueError`,
+and the values of ``math.atan2(b, a)`` and ``cmath.phase(complex(a, b))`` always
+match.  Contributed by High Performance Kernels LLC.