bpo-46431: improve error message on invalid calls to BaseExceptionGroup.__new__ (GH-30854)

Lib/test/test_exception_group.py

@@ -22,7 +22,7 @@ class TestExceptionGroupTypeHierarchy(unittest.TestCase):
 
 class BadConstructorArgs(unittest.TestCase):
     def test_bad_EG_construction__too_many_args(self):
-        MSG = 'function takes exactly 2 arguments'
+        MSG = 'BaseExceptionGroup.__new__\(\) takes exactly 2 arguments'
         with self.assertRaisesRegex(TypeError, MSG):
             ExceptionGroup('no errors')
         with self.assertRaisesRegex(TypeError, MSG):

Misc/NEWS.d/next/Core and Builtins/2022-01-24-16-58-01.bpo-46431.N6mKAx.rst

@@ -0,0 +1 @@
+Improve error message on invalid calls to :meth:`BaseExceptionGroup.__new__`.

Objects/exceptions.c

@@ -685,7 +685,10 @@ BaseExceptionGroup_new(PyTypeObject *type, PyObject *args, PyObject *kwds)
     PyObject *message = NULL;
     PyObject *exceptions = NULL;
 
-    if (!PyArg_ParseTuple(args, "UO", &message, &exceptions)) {
+    if (!PyArg_ParseTuple(args,
+                          "UO:BaseExceptionGroup.__new__",
+                          &message,
+                          &exceptions)) {
         return NULL;
     }