[Python-checkins] [3.7] bpo-39871: Fix possible SystemError in atan2, copysign and remainder (GH-18806) (GH-18990)

[Mark Dickinson]

https://github.com/python/cpython/commit/4dcfe5f2e4bad8e03990de75d8d4ec20e8aa23b3
commit: 4dcfe5f2e4bad8e03990de75d8d4ec20e8aa23b3
branch: 3.7
author: Mark Dickinson <mdickinson at enthought.com>
committer: GitHub <noreply at github.com>
date: 2020-03-14T11:51:53Z
summary:

[3.7] bpo-39871: Fix possible SystemError in atan2, copysign and remainder (GH-18806) (GH-18990)

In math_2(), the first PyFloat_AsDouble() call should be checked
for failure before the second call.

Co-authored-by: Mark Dickinson <dickinsm at gmail.com>.
(cherry picked from commit 5208b4b37953a406db0ed6a9db545c2948dde989)

Co-authored-by: Zackery Spytz <zspytz at gmail.com>

files:
A Misc/NEWS.d/next/Core and Builtins/2020-03-06-06-12-37.bpo-39871.dCAj_2.rst
M Lib/test/test_math.py
M Modules/mathmodule.c

diff --git a/Lib/test/test_math.py b/Lib/test/test_math.py
index 44785d3e49a25..4a61260f0453c 100644
--- a/Lib/test/test_math.py
+++ b/Lib/test/test_math.py
@@ -1415,6 +1415,22 @@ def test_mtestfile(self):
             self.fail('Failures in test_mtestfile:\n  ' +
                       '\n  '.join(failures))
 
+    def test_issue39871(self):
+        # A SystemError should not be raised if the first arg to atan2(),
+        # copysign(), or remainder() cannot be converted to a float.
+        class F:
+            def __float__(self):
+                self.converted = True
+                1/0
+        for func in math.atan2, math.copysign, math.remainder:
+            y = F()
+            with self.assertRaises(TypeError):
+                func("not a number", y)
+
+            # There should not have been any attempt to convert the second
+            # argument to a float.
+            self.assertFalse(getattr(y, "converted", False))
+
     # Custom assertions.
 
     def assertIsNaN(self, value):
diff --git a/Misc/NEWS.d/next/Core and Builtins/2020-03-06-06-12-37.bpo-39871.dCAj_2.rst b/Misc/NEWS.d/next/Core and Builtins/2020-03-06-06-12-37.bpo-39871.dCAj_2.rst
new file mode 100644
index 0000000000000..0b4c2e5f4cc92
--- /dev/null
+++ b/Misc/NEWS.d/next/Core and Builtins/2020-03-06-06-12-37.bpo-39871.dCAj_2.rst	
@@ -0,0 +1,3 @@
+Fix a possible :exc:`SystemError` in ``math.{atan2,copysign,remainder}()``
+when the first argument cannot be converted to a :class:`float`. Patch by
+Zachary Spytz.
diff --git a/Modules/mathmodule.c b/Modules/mathmodule.c
index 8eedca8a30b95..8bf0ab0bcb11f 100644
--- a/Modules/mathmodule.c
+++ b/Modules/mathmodule.c
@@ -1004,9 +1004,13 @@ math_2(PyObject *args, double (*func) (double, double), const char *funcname)
     if (! PyArg_UnpackTuple(args, funcname, 2, 2, &ox, &oy))
         return NULL;
     x = PyFloat_AsDouble(ox);
+    if (x == -1.0 && PyErr_Occurred()) {
+        return NULL;
+    }
     y = PyFloat_AsDouble(oy);
-    if ((x == -1.0 || y == -1.0) && PyErr_Occurred())
+    if (y == -1.0 && PyErr_Occurred()) {
         return NULL;
+    }
     errno = 0;
     PyFPE_START_PROTECT("in math_2", return 0);
     r = (*func)(x, y);