gh-103590: do not wrap a single exception raised from a try-except* (#103665)

Doc/whatsnew/3.12.rst

@@ -237,6 +237,11 @@ Other Language Changes
   wrapped by a :exc:`RuntimeError`. Context information is added to the
   exception as a :pep:`678` note. (Contributed by Irit Katriel in :gh:`77757`.)
 
+* When a ``try-except*`` construct handles the entire :exc:`ExceptionGroup`
+  and raises one other exception, that exception is no longer wrapped in an
+  :exc:`ExceptionGroup`. (Contributed by Irit Katriel in :gh:`103590`.)
+
+
 New Modules
 ===========
 

Lib/test/test_except_star.py

@@ -618,18 +618,17 @@ class TestExceptStarRaise(ExceptStarTest):
                 raise orig
             except* (TypeError, ValueError) as e:
                 raise SyntaxError(3)
-        except BaseException as e:
+        except SyntaxError as e:
             exc = e
 
-        self.assertExceptionIsLike(
+        self.assertExceptionIsLike(exc, SyntaxError(3))
-            exc, ExceptionGroup("", [SyntaxError(3)]))
 
         self.assertExceptionIsLike(
-            exc.exceptions[0].__context__,
+            exc.__context__,
             ExceptionGroup("eg", [TypeError(1), ValueError(2)]))
 
         self.assertMetadataNotEqual(orig, exc)
-        self.assertMetadataEqual(orig, exc.exceptions[0].__context__)
+        self.assertMetadataEqual(orig, exc.__context__)
 
     def test_raise_handle_all_raise_one_unnamed(self):
         orig = ExceptionGroup("eg", [TypeError(1), ValueError(2)])
@@ -638,18 +637,17 @@ class TestExceptStarRaise(ExceptStarTest):
                 raise orig
             except* (TypeError, ValueError) as e:
                 raise SyntaxError(3)
-        except ExceptionGroup as e:
+        except SyntaxError as e:
             exc = e
 
-        self.assertExceptionIsLike(
+        self.assertExceptionIsLike(exc, SyntaxError(3))
-            exc, ExceptionGroup("", [SyntaxError(3)]))
 
         self.assertExceptionIsLike(
-            exc.exceptions[0].__context__,
+            exc.__context__,
             ExceptionGroup("eg", [TypeError(1), ValueError(2)]))
 
         self.assertMetadataNotEqual(orig, exc)
-        self.assertMetadataEqual(orig, exc.exceptions[0].__context__)
+        self.assertMetadataEqual(orig, exc.__context__)
 
     def test_raise_handle_all_raise_two_named(self):
         orig = ExceptionGroup("eg", [TypeError(1), ValueError(2)])
@@ -773,23 +771,22 @@ class TestExceptStarRaiseFrom(ExceptStarTest):
                 raise orig
             except* (TypeError, ValueError) as e:
                 raise SyntaxError(3) from e
-        except BaseException as e:
+        except SyntaxError as e:
             exc = e
 
-        self.assertExceptionIsLike(
+        self.assertExceptionIsLike(exc, SyntaxError(3))
-            exc, ExceptionGroup("", [SyntaxError(3)]))
 
         self.assertExceptionIsLike(
-            exc.exceptions[0].__context__,
+            exc.__context__,
             ExceptionGroup("eg", [TypeError(1), ValueError(2)]))
 
         self.assertExceptionIsLike(
-            exc.exceptions[0].__cause__,
+            exc.__cause__,
             ExceptionGroup("eg", [TypeError(1), ValueError(2)]))
 
         self.assertMetadataNotEqual(orig, exc)
-        self.assertMetadataEqual(orig, exc.exceptions[0].__context__)
+        self.assertMetadataEqual(orig, exc.__context__)
-        self.assertMetadataEqual(orig, exc.exceptions[0].__cause__)
+        self.assertMetadataEqual(orig, exc.__cause__)
 
     def test_raise_handle_all_raise_one_unnamed(self):
         orig = ExceptionGroup("eg", [TypeError(1), ValueError(2)])
@@ -799,23 +796,22 @@ class TestExceptStarRaiseFrom(ExceptStarTest):
             except* (TypeError, ValueError) as e:
                 e = sys.exception()
                 raise SyntaxError(3) from e
-        except ExceptionGroup as e:
+        except SyntaxError as e:
             exc = e
 
-        self.assertExceptionIsLike(
+        self.assertExceptionIsLike(exc, SyntaxError(3))
-            exc, ExceptionGroup("", [SyntaxError(3)]))
 
         self.assertExceptionIsLike(
-            exc.exceptions[0].__context__,
+            exc.__context__,
             ExceptionGroup("eg", [TypeError(1), ValueError(2)]))
 
         self.assertExceptionIsLike(
-            exc.exceptions[0].__cause__,
+            exc.__cause__,
             ExceptionGroup("eg", [TypeError(1), ValueError(2)]))
 
         self.assertMetadataNotEqual(orig, exc)
-        self.assertMetadataEqual(orig, exc.exceptions[0].__context__)
+        self.assertMetadataEqual(orig, exc.__context__)
-        self.assertMetadataEqual(orig, exc.exceptions[0].__cause__)
+        self.assertMetadataEqual(orig, exc.__cause__)
 
     def test_raise_handle_all_raise_two_named(self):
         orig = ExceptionGroup("eg", [TypeError(1), ValueError(2)])

Misc/NEWS.d/next/Core and Builtins/2023-04-21-16-12-41.gh-issue-103590.7DHDOE.rst

@@ -0,0 +1 @@
+Do not wrap a single exception raised from a ``try-except*`` construct in an :exc:`ExceptionGroup`.

Objects/exceptions.c

@@ -1421,7 +1421,12 @@ _PyExc_PrepReraiseStar(PyObject *orig, PyObject *excs)
         if (res < 0) {
             goto done;
         }
-        result = _PyExc_CreateExceptionGroup("", raised_list);
+        if (PyList_GET_SIZE(raised_list) > 1) {
+            result = _PyExc_CreateExceptionGroup("", raised_list);
+        }
+        else {
+            result = Py_NewRef(PyList_GetItem(raised_list, 0));
+        }
         if (result == NULL) {
             goto done;
         }