gh-139551: add support for BaseExceptionGroup in IDLE

Lib/idlelib/run.py

@@ -249,31 +249,73 @@ def print_exception():
     sys.last_type, sys.last_value, sys.last_traceback = excinfo
     sys.last_exc = val
     seen = set()
+    exclude = ("run.py", "rpc.py", "threading.py", "queue.py",
+               "debugger_r.py", "bdb.py")
 
-    def print_exc(typ, exc, tb):
+    def print_exc_group(typ, exc, tb, prefix=""):
+        prefix2 = prefix or "  "
+        if tb:
+            if not prefix:
+                print("  + Exception Group Traceback (most recent call last):", file=efile)
+            else:
+                print(f"{prefix}| Exception Group Traceback (most recent call last):", file=efile)
+            tbe = traceback.extract_tb(tb)
+            cleanup_traceback(tbe, exclude)
+            for line in traceback.format_list(tbe):
+                for subline in line.rstrip().splitlines():
+                    print(f"{prefix2}| {subline}", file=efile)
+        lines = get_message_lines(typ, exc, tb)
+        for line in lines:
+            print(f"{prefix2}| {line}", end="", file=efile)
+        for i, sub in enumerate(exc.exceptions, 1):
+            if i == 1:
+                first_line_pre = "+-"
+            else:
+                first_line_pre = "  "
+            print(f"{prefix2}{first_line_pre}+---------------- {i} ----------------", file=efile)
+            if id(sub) not in seen:
+                if not prefix:
+                    print_exc(type(sub), sub, sub.__traceback__, "    ")
+                else:
+                    print_exc(type(sub), sub, sub.__traceback__, prefix + "  ")
+                need_print_underline = not isinstance(sub, BaseExceptionGroup)
+            else:
+                print(f"{prefix2}  | <exception {type(sub).__name__} has printed>")
+                need_print_underline = True
+            if need_print_underline:
+                print(f"{prefix2}  +------------------------------------", file=efile)
+
+    def print_exc(typ, exc, tb, prefix=""):
         seen.add(id(exc))
         context = exc.__context__
         cause = exc.__cause__
+        prefix2 = f"{prefix}| " if prefix else ""
         if cause is not None and id(cause) not in seen:
-            print_exc(type(cause), cause, cause.__traceback__)
-            print("\nThe above exception was the direct cause "
-                  "of the following exception:\n", file=efile)
+            print_exc(type(cause), cause, cause.__traceback__, prefix)
+            print(f"{prefix2}\n{prefix2}The above exception was the direct cause "
+                  f"of the following exception:\n{prefix2}", file=efile)
         elif (context is not None and
               not exc.__suppress_context__ and
               id(context) not in seen):
-            print_exc(type(context), context, context.__traceback__)
-            print("\nDuring handling of the above exception, "
-                  "another exception occurred:\n", file=efile)
-        if tb:
-            tbe = traceback.extract_tb(tb)
-            print('Traceback (most recent call last):', file=efile)
-            exclude = ("run.py", "rpc.py", "threading.py", "queue.py",
-                       "debugger_r.py", "bdb.py")
-            cleanup_traceback(tbe, exclude)
-            traceback.print_list(tbe, file=efile)
-        lines = get_message_lines(typ, exc, tb)
-        for line in lines:
-            print(line, end='', file=efile)
+            print_exc(type(context), context, context.__traceback__, prefix)
+            print(f"{prefix2}\n{prefix2}During handling of the above exception, "
+                  f"another exception occurred:\n{prefix2}", file=efile)
+        if isinstance(exc, BaseExceptionGroup):
+            print_exc_group(typ, exc, tb, prefix=prefix)
+        else:
+            if tb:
+                print(f"{prefix2}Traceback (most recent call last):", file=efile)
+                tbe = traceback.extract_tb(tb)
+                cleanup_traceback(tbe, exclude)
+                if prefix:
+                    for line in traceback.format_list(tbe):
+                        for subline in line.rstrip().splitlines():
+                            print(f"{prefix}| {subline}", file=efile)
+                else:
+                    traceback.print_list(tbe, file=efile)
+            lines = get_message_lines(typ, exc, tb)
+            for line in lines:
+                print(f"{prefix2}{line}", end="", file=efile)
 
     print_exc(typ, val, tb)
 

Misc/NEWS.d/next/IDLE/2025-10-05-19-33-39.gh-issue-139551.TX9BRc.rst

@@ -0,0 +1 @@
+Support rendering :exc:`BaseExceptionGroup` in IDLE.