Raise a TypeError if conflicting positional and named arguments are

passed to a Structure or Union constructor.

Lib/ctypes/test/test_structures.py

@@ -215,6 +215,15 @@ class StructureTestCase(unittest.TestCase):
         # too long
         self.assertRaises(ValueError, Person, "1234567", 5)
 
+    def test_conflicting_initializers(self):
+        class POINT(Structure):
+            _fields_ = [("x", c_int), ("y", c_int)]
+        # conflicting positional and keyword args
+        self.assertRaises(TypeError, POINT, 2, 3, x=4)
+        self.assertRaises(TypeError, POINT, 2, 3, y=4)
+
+        # Should this raise TypeError instead?
+        self.assertRaises(ValueError, POINT, 2, 3, 4)
 
     def test_keyword_initializers(self):
         class POINT(Structure):

Misc/NEWS

@@ -364,6 +364,9 @@ Core and builtins
 Library
 -------
 
+- Issue #1831: ctypes now raises a TypeError if conflicting positional
+  and named arguments are passed to a Structure or Union initializer.
+
 - Convert the internal ctypes array type cache to a WeakValueDict so
   that array types do not live longer than needed.
 

Modules/_ctypes/_ctypes.c

@@ -3578,6 +3578,21 @@ Struct_init(PyObject *self, PyObject *args, PyObject *kwds)
 				return IBUG("_fields_[i][0] failed");
 			}
 
+			if (kwds && PyDict_GetItem(kwds, name)) {
+				char *field = PyString_AsString(name);
+				if (field == NULL) {
+					PyErr_Clear();
+					field = "???";
+				}
+				PyErr_Format(PyExc_TypeError,
+					     "duplicate values for field %s",
+					     field);
+				Py_DECREF(pair);
+				Py_DECREF(name);
+				Py_DECREF(fields);
+				return -1;
+			}
+
 			val = PyTuple_GET_ITEM(args, i);
 			if (-1 == PyObject_SetAttr(self, name, val)) {
 				Py_DECREF(pair);