gh-143811: Add helpful default error messages to AttributeError and NameError

Lib/test/test_exceptions.py

@@ -2003,6 +2003,25 @@ class TestClass:
 
         self.assertRaises(NameError, f)
 
+    def test_gh_143811(self):
+        def f():
+            span = 42
+            try:
+                spam
+            except NameError as exc:
+                # Clear the message.
+                exc.args = ()
+                raise
+
+        try:
+            f()
+        except NameError:
+            with support.captured_stderr() as err:
+                sys.__excepthook__(*sys.exc_info())
+
+        # 'spam' should appear even when message was empty.
+        self.assertIn("name 'spam' is not defined", err.getvalue())
+
     # Note: name suggestion tests live in `test_traceback`.
 
 
@@ -2046,6 +2065,24 @@ def blech(self):
             self.assertEqual("bluch", exc.name)
             self.assertEqual(obj, exc.obj)
 
+    def test_gh_143811(self):
+        def f():
+            class A:
+                def __getattr__(self, attr):
+                    # Provide no message.
+                    raise AttributeError
+
+            A().bluch
+
+        try:
+            f()
+        except AttributeError:
+            with support.captured_stderr() as err:
+                sys.__excepthook__(*sys.exc_info())
+
+        # Should appear even when no message was provided.
+        self.assertIn("'A' object has no attribute 'bluch'", err.getvalue())
+
     # Note: name suggestion tests live in `test_traceback`.
 
 

Lib/test/test_traceback.py

@@ -4259,6 +4259,7 @@ def __getattr__(self, attr):
                 raise AttributeError()
 
         actual = self.get_suggestion(A(), 'bluch')
+        self.assertIn("'A' object has no attribute 'bluch'.", actual)
         self.assertIn("blech", actual)
 
         class A:
@@ -4267,6 +4268,7 @@ def __getattr__(self, attr):
                 raise AttributeError
 
         actual = self.get_suggestion(A(), 'bluch')
+        self.assertIn("'A' object has no attribute 'bluch'.", actual)
         self.assertIn("blech", actual)
 
     def test_suggestions_invalid_args(self):
@@ -4930,6 +4932,18 @@ def func():
         actual = self.get_suggestion(func)
         self.assertIn("forget to import '_io'", actual)
 
+    def test_name_error_empty(self):
+        """See GH-143811."""
+        def func():
+            span = 42
+            try:
+                spam
+            except NameError as exc:
+                exc.args = ()
+                raise
+        actual = self.get_suggestion(func)
+        self.assertIn("name 'spam' is not defined", actual)
+        self.assertIn("Did you mean: 'span'?", actual)
 
 
 class PurePythonSuggestionFormattingTests(

Lib/traceback.py

@@ -1125,9 +1125,15 @@ def __init__(self, exc_type, exc_value, exc_traceback, *, limit=None,
                     + "add the site-packages directory to sys.path "
                     + "or to enable your virtual environment?")
         elif exc_type and issubclass(exc_type, (NameError, AttributeError)) and \
-                getattr(exc_value, "name", None) is not None:
-            wrong_name = getattr(exc_value, "name", None)
+                (wrong_name := getattr(exc_value, "name", None)) is not None:
             suggestion = _compute_suggestion_error(exc_value, exc_traceback, wrong_name)
+            if not self._str:
+                if issubclass(exc_type, AttributeError):
+                    if (obj_type := type(getattr(exc_value, "obj", None))) is not type(None):
+                        obj_type_name = object.__getattribute__(obj_type, "__name__")
+                        self._str = f"{obj_type_name!r} object has no attribute {wrong_name!r}"
+                else:  # NameError
+                    self._str = f"name {wrong_name!r} is not defined"
             if suggestion:
                 self._str += f". Did you mean: '{suggestion}'?"
             if issubclass(exc_type, NameError):

Misc/NEWS.d/next/Library/2026-01-13-19-51-37.gh-issue-143811.PLHsyK.rst

@@ -0,0 +1,3 @@
+:exc:`AttributeError` and :exc:`NameError` exceptions raised with no message
+now get helpful default messages when displaying traceback. Patch by Bartosz
+Sławecki.