gh-143811: Add helpful default error messages to `AttributeError` and `NameError` #143813

Original file line number	Diff line number	Diff line change
Expand Up		@@ -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`.


Expand Down Expand Up		@@ -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`.


Expand Down

14 changes: 14 additions & 0 deletions Lib/test/test_traceback.py

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Original file line number	Diff line number	Diff line change
Expand Up		@@ -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:
Expand All		@@ -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):
Expand Down Expand Up		@@ -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(
Expand Down

10 changes: 8 additions & 2 deletions Lib/traceback.py

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Original file line number	Diff line number	Diff line change
Expand Up		@@ -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:
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		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):
Expand Down

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Original file line number	Diff line number	Diff line change
		@@ -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.

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