assertion failure in PyErr_WriteUnraisable() in case of an exception with a bad __module__

[orenmn]

BPO	31418
Nosy	@serhiy-storchaka, @orenmn
PRs	bpo-31418: Fix an assertion failure in case of an exception with a bad __module__ attribute #3539 [3.6] bpo-31418: Fix an assertion failure in PyErr_WriteUnraisable() in case of an exception with a bad __module__ attribute. (GH-3539) #3556

^{Note: these values reflect the state of the issue at the time it was migrated and might not reflect the current state.}

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GitHub fields:

assignee = None
closed_at = <Date 2017-09-14.06:42:14.343>
created_at = <Date 2017-09-11.12:49:19.794>
labels = ['interpreter-core', '3.7', 'type-crash']
title = 'assertion failure in PyErr_WriteUnraisable() in case of an exception with a bad __module__'
updated_at = <Date 2017-09-14.06:42:14.342>
user = 'https://github.com/orenmn'

bugs.python.org fields:

activity = <Date 2017-09-14.06:42:14.342>
actor = 'serhiy.storchaka'
assignee = 'none'
closed = True
closed_date = <Date 2017-09-14.06:42:14.343>
closer = 'serhiy.storchaka'
components = ['Interpreter Core']
creation = <Date 2017-09-11.12:49:19.794>
creator = 'Oren Milman'
dependencies = []
files = []
hgrepos = []
issue_num = 31418
keywords = ['patch']
message_count = 7.0
messages = ['301872', '301873', '301874', '302042', '302047', '302126', '302145']
nosy_count = 2.0
nosy_names = ['serhiy.storchaka', 'Oren Milman']
pr_nums = ['3539', '3556']
priority = 'normal'
resolution = 'fixed'
stage = 'resolved'
status = 'closed'
superseder = None
type = 'crash'
url = 'https://bugs.python.org/issue31418'
versions = ['Python 3.6', 'Python 3.7']

[orenmn]

The following code causes an assertion failure in PyErr_WriteUnraisable() (in
Python/errors.c):

class BadException(Exception):
    __module__ = None

class BadClass:
    def __del__(self):
        raise BadException

foo = BadClass()
del foo

this is because PyErr_WriteUnraisable() assumes that __module__ is a string,
and passes it to _PyUnicode_EqualToASCIIId(), which asserts it received a string.

what is the wanted behavior in such a case?
should we ignore the bad __module__ and print '<unknown>' as the module name
in the traceback?

[serhiy-storchaka]

Printing '<unknown>' LGTM.

Implicit converting to str can raise a warning or exception if __module__ is a bytes object.

[serhiy-storchaka]

I think this patch doesn't need a test (which would require using a subprocess).

[orenmn]

what do you mean by 'Implicit converting to str can raise a warning or exception if __module__ is a bytes object.'?

should we treat __module__ differently in case it is a bytes object?

[serhiy-storchaka]

PyFile_WriteObject(moduleName, f, Py_PRINT_RAW) implicitly converts its argument to string. I mean that treating non-string moduleName the same way as string moduleName not equal to string "builtins" and calling PyFile_WriteObject() would cause other problem. Treating non-string moduleName the same way as moduleName==NULL LGTM.

[serhiy-storchaka]

New changeset f6e61df by Serhiy Storchaka (Oren Milman) in branch 'master':
bpo-31418: Fix an assertion failure in PyErr_WriteUnraisable() in case of an exception with a bad __module__ attribute. (bpo-3539)
f6e61df

[serhiy-storchaka]

New changeset 5dbb28e by Serhiy Storchaka (Miss Islington (bot)) in branch '3.6':
[3.6] bpo-31418: Fix an assertion failure in PyErr_WriteUnraisable() in case of an exception with a bad __module__ attribute. (GH-3539) (bpo-3556)
5dbb28e