Bug report

Whennotes on an exception cannot be shown because therepr andstr raise exceptions, a<note str() failed> message is shown instead. In the case whereexception.__notes__ is not a sequence and cannot be shown, a<__notes__ repr() failed> is shown. In the second case, the message does not include a trailing newline.

__notes__ is a list containing a broken "note" - output includes a newline:

classA:def__repr__(self):raiseException()e=Exception()e.__notes__= [A()]# !!!raisee

user@host $ ./repro.pyTraceback (most recent call last):  File "./repro.py", line 8, in <module>    raise eException<note str() failed>user@host $

__notes__ is just a single broken "note" - output does not include a newline:

classA:def__repr__(self):raiseException()e=Exception()e.__notes__=A()# !!!raisee

user@host $ ./repro.pyTraceback (most recent call last):  File "./repro.py", line 8, in <module>    raise eException<__notes__ repr() failed>user@host $

Additionally, when__notes__ is a string/bytes, the contents are expoded over multiple lines because of anisinstance(__notes__, Sequence) check.

String:

e=Exception()e.__notes__="a note"raisee

user@host $ ./repro.pyTraceback (most recent call last):  File "./repro.py", line 8, in <module>    raise eExceptionanoteuser@host $

Bytes:

e=Exception()e.__notes__=b"a note"raisee

user@host $ ./repro.pyTraceback (most recent call last):  File "./repro.py", line 8, in <module>    raise eException9732110111116101user@host $

Even though the above are all edge cases, since there are some checks that handle these cases already, it makes sense to handle them more gracefully.

Your environment

• CPython versions tested on: 3.12.0a7+
• Operating system and architecture: macOS Mojave (x86)

Linked PRs

• gh-103895: Improve how invalidException.__notes__ are displayed #103897