if __notes__ is not sequence, print repr(__notes__). If note is not a…

… string, print str(note)
python · iritkatriel · Apr 16, 2022 · Feb 13, 2022 · Feb 23, 2022 · Mar 2, 2022
commit 614378e465087f5529eed26d3a63c73de3b399f6
diff --git a/Lib/test/test_traceback.py b/Lib/test/test_traceback.py
@@ -1323,7 +1323,7 @@ def test_syntax_error_various_offsets(self):
                 self.assertEqual(exp, err)
 
     def test_exception_with_note(self):
-        e = ValueError(42)
+        e = ValueError(123)
         vanilla = self.get_report(e)
 
         e.add_note('My Note')
@@ -1340,13 +1340,40 @@ def test_exception_with_note(self):
         del e.__notes__
         self.assertEqual(self.get_report(e), vanilla)
 
-        # non-sequence __notes__ is ignored
-        e.__notes__ = 42
-        self.assertEqual(self.get_report(e), vanilla)
+    def test_exception_with_invalid_notes(self):
+        e = ValueError(123)
+        vanilla = self.get_report(e)
+
+        # non-sequence __notes__
+        class BadThing:
+            def __str__(self):
+                return 'bad str'
+
+            def __repr__(self):
+                return 'bad repr'
+
+        # unprintable, non-sequence __notes__
+        class Unprintable:
+            def __repr__(self):
+                raise ValueError('bad value')
+
+        e.__notes__ = BadThing()
+        notes_repr = 'bad repr'
+        self.assertEqual(self.get_report(e), vanilla + notes_repr)
+
+        e.__notes__ = Unprintable()
+        err_msg = '<__notes__ repr() failed>'
+        self.assertEqual(self.get_report(e), vanilla + err_msg)
+
+        # non-string item in the __notes__ sequence
+        e.__notes__  = [BadThing(), 'Final Note']
+        bad_note = 'bad str'
+        self.assertEqual(self.get_report(e), vanilla + bad_note + '\nFinal Note\n')
 
-        # non-string items in the __notes__ sequence are ignored
-        e.__notes__  = [42, 'Final Note']
-        self.assertEqual(self.get_report(e), vanilla + 'Final Note\n')
+        # unprintable, non-string item in the __notes__ sequence
+        e.__notes__  = [Unprintable(), 'Final Note']
+        err_msg = '<note str() failed>'
+        self.assertEqual(self.get_report(e), vanilla + err_msg + '\nFinal Note\n')
 
     def test_exception_with_note_with_multiple_notes(self):
         e = ValueError(42)

diff --git a/Lib/traceback.py b/Lib/traceback.py
@@ -163,18 +163,18 @@ def format_exception_only(exc, /, value=_sentinel):
 # -- not official API but folk probably use these two functions.
 
 def _format_final_exc_line(etype, value):
-    valuestr = _some_str(value)
+    valuestr = _safe_string(value, 'exception')
     if value is None or not valuestr:
         line = "%s\n" % etype
     else:
         line = "%s: %s\n" % (etype, valuestr)
     return line
 
-def _some_str(value):
+def _safe_string(value, what, func=str):
     try:
-        return str(value)
+        return func(value)
     except:
-        return '<exception str() failed>'
+        return f'<{what} {func.__name__}() failed>'
 
 # --
 
@@ -688,7 +688,7 @@ def __init__(self, exc_type, exc_value, exc_traceback, *, limit=None,
         self.exc_type = exc_type
         # Capture now to permit freeing resources: only complication is in the
         # unofficial API _format_final_exc_line
-        self._str = _some_str(exc_value)
+        self._str = _safe_string(exc_value, 'exception')
         self.__notes__ = getattr(exc_value, '__notes__', None)
 
         if exc_type and issubclass(exc_type, SyntaxError):
@@ -824,8 +824,11 @@ def format_exception_only(self):
             yield from self._format_syntax_error(stype)
         if isinstance(self.__notes__, collections.abc.Sequence):
             for note in self.__notes__:
-                if isinstance(note, str):
-                    yield from [l + '\n' for l in note.split('\n')]
+                if not isinstance(note, str):
+                    note = _safe_string(note, 'note')
+                yield from [l + '\n' for l in note.split('\n')]
+        elif self.__notes__ is not None:
+            yield _safe_string(self.__notes__, '__notes__', func=repr)
 
     def _format_syntax_error(self, stype):
         """Format SyntaxError exceptions (internal helper)."""

@@ -1145,8 +1145,21 @@ print_exception_notes(struct exception_print_context *ctx, PyObject *value)
         return -1;
     }
     if (!PySequence_Check(notes)) {
+        int res = 0;
+        if (write_indented_margin(ctx, f) < 0) {
+            res = -1;
+        }
+        PyObject *s = PyObject_Repr(notes);
+        if (s == NULL) {
+            PyErr_Clear();
+            res = PyFile_WriteString("<__notes__ repr() failed>", f);
+        }
+        else {
+            res = PyFile_WriteObject(s, f, Py_PRINT_RAW);
+            Py_DECREF(s);
+        }
         Py_DECREF(notes);
-        return 0;
+        return res;
     }
     Py_ssize_t num_notes = PySequence_Length(notes);
     PyObject *lines = NULL;
@@ -1176,8 +1189,27 @@ print_exception_notes(struct exception_print_context *ctx, PyObject *value)
             Py_CLEAR(lines);
         }
         else {
-            /* Ignore notes which are not strings */
+            int res = 0;
+            if (write_indented_margin(ctx, f) < 0) {
+                res = -1;
+            }
+            PyObject *s = PyObject_Str(note);
+            if (s == NULL) {
+                PyErr_Clear();
+                res = PyFile_WriteString("<note str() failed>", f);
+            }
+            else {
+                res = PyFile_WriteObject(s, f, Py_PRINT_RAW);
+                Py_DECREF(s);
+            }
             Py_DECREF(note);
+            if (res < 0) {
+                goto error;
+            }
+            if (PyFile_WriteString("\n", f) < 0) {
+                goto error;
+            }
+
         }
     }