[3.11] gh-113358: Fix rendering tracebacks with exceptions with a broken __getattr__ (GH-113359)

Lib/test/test_traceback.py

@@ -1601,6 +1601,21 @@ def __repr__(self):
  err_msg = '<note str() failed>'
  self.assertEqual(self.get_report(e), vanilla + err_msg + '\nFinal Note\n')
 
+ # an exception with a broken __getattr__ raising a non expected error
+ class BrokenException(Exception):
+ broken = False
+ def __getattr__(self, name):
+ if self.broken:
+ raise ValueError(f'no {name}')
+ raise AttributeError(name)
+
+ e = BrokenException(123)
+ vanilla = self.get_report(e)
+ e.broken = True
+ self.assertEqual(
+ self.get_report(e),
+ vanilla + "Ignored error getting __notes__: ValueError('no __notes__')\n")
+
  def test_exception_with_multiple_notes(self):
  for e in [ValueError(42), SyntaxError('bad syntax')]:
  with self.subTest(e=e):

Lib/traceback.py

@@ -733,7 +733,11 @@ def __init__(self, exc_type, exc_value, exc_traceback, *, limit=None,
  # Capture now to permit freeing resources: only complication is in the
  # unofficial API _format_final_exc_line
  self._str = _safe_string(exc_value, 'exception')
- self.__notes__ = getattr(exc_value, '__notes__', None)
+ try:
+ self.__notes__ = getattr(exc_value, '__notes__', None)
+ except Exception as e:
+ self.__notes__ = [
+ f'Ignored error getting __notes__: {_safe_string(e, "__notes__", repr)}']
 
  if exc_type and issubclass(exc_type, SyntaxError):
  # Handle SyntaxError's specially

Misc/NEWS.d/next/Library/2023-12-21-14-55-06.gh-issue-113358.nRkiSL.rst

@@ -0,0 +1 @@
+Fix rendering tracebacks for exceptions with a broken ``__getattr__``.

Python/pythonrun.c

@@ -1199,6 +1199,36 @@ print_exception_notes(struct exception_print_context *ctx, PyObject *notes)
  return -1;
 }
 
+static int
+get_exception_notes(struct exception_print_context *ctx, PyObject *value, PyObject **notes) {
+ PyObject *note = NULL;
+
+ if (_PyObject_LookupAttr(value, &_Py_ID(__notes__), notes) < 0) {
+ PyObject *type, *errvalue, *tback;
+ PyErr_Fetch(&type, &errvalue, &tback);
+ note = PyUnicode_FromFormat("Ignored error getting __notes__: %R", errvalue);
+ Py_XDECREF(type);
+ Py_XDECREF(errvalue);
+ Py_XDECREF(tback);
+ if (!note) {
+ goto error;
+ }
+ *notes = PyList_New(1);
+ if (!*notes) {
+ goto error;
+ }
+ if (PyList_SetItem(*notes, 0, note) < 0) {
+ Py_DECREF(*notes);
+ goto error;
+ }
+ }
+
+ return 0;
+error:
+ Py_XDECREF(note);
+ return -1;
+}
+
 static int
 print_exception(struct exception_print_context *ctx, PyObject *value)
 {
@@ -1218,7 +1248,7 @@ print_exception(struct exception_print_context *ctx, PyObject *value)
 
  /* grab the type and notes now because value can change below */
  PyObject *type = (PyObject *) Py_TYPE(value);
- if (_PyObject_LookupAttr(value, &_Py_ID(__notes__), &notes) < 0) {
+ if (get_exception_notes(ctx, value, &notes) < 0) {
  goto error;
  }