[3.11] gh-103590: do not wrap a single exception raised from a try-except* (#104094)

Author: iritkatriel

Doc/reference/compound_stmts.rst

@@ -365,6 +365,10 @@ Any remaining exceptions that were not handled by any :keyword:`!except*`
 clause are re-raised at the end, combined into an exception group along with
 all exceptions that were raised from within :keyword:`!except*` clauses.
 
+From version 3.11.4, when the entire :exc:`ExceptionGroup` is handled and
+only one exception is raised from an :keyword:`!except*` clause, this
+exception is no longer wrapped to form a new :exc:`ExceptionGroup`.
+
 If the raised exception is not an exception group and its type matches
 one of the :keyword:`!except*` clauses, it is caught and wrapped by an
 exception group with an empty message string. ::

Lib/test/test_except_star.py

@@ -636,18 +636,17 @@ def test_raise_handle_all_raise_one_named(self):
                 raise orig
             except* (TypeError, ValueError) as e:
                 raise SyntaxError(3)
-        except BaseException as e:
+        except SyntaxError as e:
             exc = e
 
-        self.assertExceptionIsLike(
-            exc, ExceptionGroup("", [SyntaxError(3)]))
+        self.assertExceptionIsLike(exc, 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)])
@@ -656,18 +655,17 @@ def test_raise_handle_all_raise_one_unnamed(self):
                 raise orig
             except* (TypeError, ValueError) as e:
                 raise SyntaxError(3)
-        except ExceptionGroup as e:
+        except SyntaxError as e:
             exc = e
 
-        self.assertExceptionIsLike(
-            exc, ExceptionGroup("", [SyntaxError(3)]))
+        self.assertExceptionIsLike(exc, 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)])
@@ -791,23 +789,22 @@ def test_raise_handle_all_raise_one_named(self):
                 raise orig
             except* (TypeError, ValueError) as e:
                 raise SyntaxError(3) from e
-        except BaseException as e:
+        except SyntaxError as e:
             exc = e
 
-        self.assertExceptionIsLike(
-            exc, ExceptionGroup("", [SyntaxError(3)]))
+        self.assertExceptionIsLike(exc, 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.exceptions[0].__cause__)
+        self.assertMetadataEqual(orig, exc.__context__)
+        self.assertMetadataEqual(orig, exc.__cause__)
 
     def test_raise_handle_all_raise_one_unnamed(self):
         orig = ExceptionGroup("eg", [TypeError(1), ValueError(2)])
@@ -817,23 +814,22 @@ def test_raise_handle_all_raise_one_unnamed(self):
             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(
-            exc, ExceptionGroup("", [SyntaxError(3)]))
+        self.assertExceptionIsLike(exc, 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.exceptions[0].__cause__)
+        self.assertMetadataEqual(orig, exc.__context__)
+        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

@@ -1423,7 +1423,12 @@ _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;
         }