Issue #24489: ensure a previously set C errno doesn't disturb cmath.polar().

2 files changed, 15 insertions, 1 deletions

diff --git a/Modules/_testcapimodule.c b/Modules/_testcapimodule.c
index 2697ac2..ba0a24b 100644
--- a/Modules/_testcapimodule.c
+++ b/Modules/_testcapimodule.c
@@ -1796,6 +1796,18 @@ raise_exception(PyObject *self, PyObject *args)
 }
 
 static PyObject *
+set_errno(PyObject *self, PyObject *args)
+{
+    int new_errno;
+
+    if (!PyArg_ParseTuple(args, "i:set_errno", &new_errno))
+        return NULL;
+
+    errno = new_errno;
+    Py_RETURN_NONE;
+}
+
+static PyObject *
 test_set_exc_info(PyObject *self, PyObject *args)
 {
     PyObject *orig_exc;
@@ -3510,6 +3522,7 @@ test_PyTime_AsMicroseconds(PyObject *self, PyObject *args)
 static PyMethodDef TestMethods[] = {
     {"raise_exception",         raise_exception,                 METH_VARARGS},
     {"raise_memoryerror",   (PyCFunction)raise_memoryerror,  METH_NOARGS},
+    {"set_errno",               set_errno,                       METH_VARARGS},
     {"test_config",             (PyCFunction)test_config,        METH_NOARGS},
     {"test_sizeof_c_types",     (PyCFunction)test_sizeof_c_types, METH_NOARGS},
     {"test_datetime_capi",  test_datetime_capi,              METH_NOARGS},
diff --git a/Modules/cmathmodule.c b/Modules/cmathmodule.c
index d12e4c5..7f6c2c9 100644
--- a/Modules/cmathmodule.c
+++ b/Modules/cmathmodule.c
@@ -986,9 +986,10 @@ cmath_polar_impl(PyModuleDef *module, Py_complex z)
 {
     double r, phi;
 
+    errno = 0;
     PyFPE_START_PROTECT("polar function", return 0)
     phi = c_atan2(z); /* should not cause any exception */
-    r = _Py_c_abs(z); /* sets errno to ERANGE on overflow;  otherwise 0 */
+    r = _Py_c_abs(z); /* sets errno to ERANGE on overflow */
     PyFPE_END_PROTECT(r)
     if (errno != 0)
         return math_error();