[3.13] gh-135511: Fixed truncated exception message for Name- and AttributeError (GH-135526) (#158276)

Only the last line of multiline error messages was displayed.
---------
(cherry picked from commit 421c411)

Co-authored-by: Locked-chess-official <13140752715@163.com>
Co-authored-by: Terry Jan Reedy <tjreedy@udel.edu>

Author: 3 people

Lib/idlelib/idle_test/test_run.py

@@ -49,14 +49,15 @@ def __eq__(self, other):
             ('int.reel', AttributeError,
                  "type object 'int' has no attribute 'reel'. "
                  "Did you mean: 'real'?\n"),
+            (r'raise NameError("123\n456")', NameError, "123\n456\n"),
             )
 
     @force_not_colorized
     def test_get_message(self):
         for code, exc, msg in self.data:
             with self.subTest(code=code):
                 try:
-                    eval(compile(code, '', 'eval'))
+                    exec(compile(code, '', 'exec'))
                 except exc:
                     typ, val, tb = sys.exc_info()
                     actual = run.get_message_lines(typ, val, tb)[0]
@@ -68,15 +69,20 @@ def test_get_message(self):
                        new_callable=lambda: (lambda t, e: None))
     def test_get_multiple_message(self, mock):
         d = self.data
-        data2 = ((d[0], d[1]), (d[1], d[2]), (d[2], d[0]))
+        data2 = ((d[0], d[1]),
+                 (d[1], d[2]),
+                 (d[2], d[3]),
+                 (d[3], d[0]),
+                 (d[1], d[3]),
+                 (d[0], d[2]))
         subtests = 0
         for (code1, exc1, msg1), (code2, exc2, msg2) in data2:
             with self.subTest(codes=(code1,code2)):
                 try:
-                    eval(compile(code1, '', 'eval'))
+                    exec(compile(code1, '', 'exec'))
                 except exc1:
                     try:
-                        eval(compile(code2, '', 'eval'))
+                        exec(compile(code2, '', 'exec'))
                     except exc2:
                         with captured_stderr() as output:
                             run.print_exception()

Lib/idlelib/run.py

@@ -4,7 +4,6 @@
 f'''{sys.executable} -c "__import__('idlelib.run').run.main()"'''
 '.run' is needed because __import__ returns idlelib, not idlelib.run.
 """
-import contextlib
 import functools
 import io
 import linecache
@@ -244,15 +243,8 @@ def show_socket_error(err, address):
 
 
 def get_message_lines(typ, exc, tb):
-    "Return line composing the exception message."
-    if typ in (AttributeError, NameError):
-        # 3.10+ hints are not directly accessible from python (#44026).
-        err = io.StringIO()
-        with contextlib.redirect_stderr(err):
-            sys.__excepthook__(typ, exc, tb)
-        return [err.getvalue().split("\n")[-2] + "\n"]
-    else:
-        return traceback.format_exception_only(typ, exc)
+    "Return lines of the exception message, with any suggestion."
+    return list(traceback.TracebackException(typ, exc, tb).format_exception_only())
 
 
 def print_exception():

Misc/NEWS.d/next/IDLE/2025-08-08-10-50-59.gh-issue-135511.9Rw5Zg.rst

@@ -0,0 +1 @@
+Fix display of :exc:`NameError` and :exc:`AttributeError` with multi-line message.