del OSError().characters_written raises SystemError

[Bachsau]

BPO	35504
Nosy	@serhiy-storchaka, @ZackerySpytz, @miss-islington, @Bachsau
PRs	bpo-35504: Fix a SystemError when delete the characters_written attribute of an OSError. #11172 bpo-35504: Fix segfaults and SystemErrors when deleting certain attrs #11175 [3.7] bpo-35504: Fix segfaults and SystemErrors when deleting certain attrs. (GH-11175) #11197 [2.7] bpo-35504: Fix segfaults and SystemErrors when deleting certain attrs. (GH-11175) #11249

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

Show more details

GitHub fields:

assignee = 'https://github.com/serhiy-storchaka'
closed_at = <Date 2018-12-17.15:28:06.032>
created_at = <Date 2018-12-14.22:22:24.790>
labels = ['interpreter-core', '3.7', '3.8']
title = '`del OSError().characters_written` raises `SystemError`'
updated_at = <Date 2018-12-20.17:38:56.688>
user = 'https://github.com/Bachsau'

bugs.python.org fields:

activity = <Date 2018-12-20.17:38:56.688>
actor = 'serhiy.storchaka'
assignee = 'serhiy.storchaka'
closed = True
closed_date = <Date 2018-12-17.15:28:06.032>
closer = 'serhiy.storchaka'
components = ['Interpreter Core']
creation = <Date 2018-12-14.22:22:24.790>
creator = 'Bachsau'
dependencies = []
files = []
hgrepos = []
issue_num = 35504
keywords = ['patch']
message_count = 10.0
messages = ['331876', '331879', '331882', '331905', '331906', '331907', '332005', '332007', '332009', '332242']
nosy_count = 4.0
nosy_names = ['serhiy.storchaka', 'ZackerySpytz', 'miss-islington', 'Bachsau']
pr_nums = ['11172', '11175', '11197', '11249']
priority = 'normal'
resolution = 'fixed'
stage = 'resolved'
status = 'closed'
superseder = None
type = None
url = 'https://bugs.python.org/issue35504'
versions = ['Python 3.7', 'Python 3.8']

[Bachsau]

del OSError().characters_written raises SystemError:
"null argument to internal routine"

I don't know why anyone should try this in productive code, but since the documentation says, that every SystemError should be reported, I'm doing that. My suggestion would be to make that attribute behave like the other ones of OSError, e.g. defaulting to None and returning to that value on deletion.

[serhiy-storchaka]

PR 11172 makes deleting characters_written to be as for other non-special attributes. Deleting it will be successful only if it was set before, and will raise an AttributeError otherwise.

>>> e = OSError()
>>> e.characters_written = 1
>>> del e.characters_written
>>> del e.characters_written
Traceback (most recent call last):
  File "<stdin>", line 1, in <module>
AttributeError: characters_written

[Bachsau]

Why is it using -1 instead of NULL as the "not-set-indicator"? -1 is a valid python integer, that can be assigned, even if it doesn't make sense in the context, while None can not, because it's missing an __index__ method.

[ZackerySpytz]

PR 11175 fixes some other related SystemErrors (and segfaults).

[serhiy-storchaka]

Why is it using -1 instead of NULL as the "not-set-indicator"?

Because the field of the C structure has integer type, and it can not be the NULL pointer.

[serhiy-storchaka]

Good catch Zackery! Thank you for your PR.

[serhiy-storchaka]

New changeset e2af34f by Serhiy Storchaka in branch 'master':
bpo-35504: Fix a SystemError when delete the characters_written attribute of an OSError. (GH-11172)
e2af34f

[serhiy-storchaka]

New changeset 842acaa by Serhiy Storchaka (Zackery Spytz) in branch 'master':
bpo-35504: Fix segfaults and SystemErrors when deleting certain attrs. (GH-11175)
842acaa

[miss-islington]

New changeset cb27284 by Miss Islington (bot) in branch '3.7':
bpo-35504: Fix segfaults and SystemErrors when deleting certain attrs. (GH-11175)
cb27284

[serhiy-storchaka]

New changeset f347c6e by Serhiy Storchaka (Zackery Spytz) in branch '2.7':
bpo-35504: Fix segfaults and SystemErrors when deleting certain attrs. (GH-11175) (GH-11249)
f347c6e