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subtype_clear can not be called from derived types #89429
Description
| BPO | 45266 |
|---|---|
| Nosy | @iritkatriel |
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 = None
created_at = <Date 2021-09-22.19:16:19.650>
labels = ['expert-C-API', 'type-bug', '3.11']
title = 'subtype_clear can not be called from derived types'
updated_at = <Date 2022-01-15.16:35:53.826>
user = 'https://bugs.python.org/VictorMilovanov'bugs.python.org fields:
activity = <Date 2022-01-15.16:35:53.826>
actor = 'iritkatriel'
assignee = 'none'
closed = False
closed_date = None
closer = None
components = ['C API']
creation = <Date 2021-09-22.19:16:19.650>
creator = 'Victor Milovanov'
dependencies = []
files = []
hgrepos = []
issue_num = 45266
keywords = []
message_count = 3.0
messages = ['402466', '402467', '410650']
nosy_count = 2.0
nosy_names = ['Victor Milovanov', 'iritkatriel']
pr_nums = []
priority = 'normal'
resolution = None
stage = None
status = 'open'
superseder = None
type = 'behavior'
url = 'https://bugs.python.org/issue45266'
versions = ['Python 3.11']
Activity
VictorMilovanov commentedon Sep 22, 2021
I am trying to define a type in C, that derives from PyTypeObject.
I want to override tp_clear. To do so properly, I should call base type's tp_clear and have it perform its cleanup steps. PyTypeObject has a tp_clear implementation: subtype_clear. Problem is, it assumes the instance it gets is of a type, that does not override PyTypeObject's tp_clear, and behaves incorrectly in 2 ways:
base = type;
while ((baseclear = base->tp_clear) == subtype_clear)
the loop condition is immediately false, as my types overrode tp_clear
VictorMilovanov commentedon Sep 22, 2021
To put it differently, if you think in terms of MRO, my custom type's MRO is
my_type_clear (from my type), subtype_clear (from PyTypeObject), etc
And subtype_clear incorrectly assumes that it is the first entry in the object's MRO list for tp_clear.
iritkatriel commentedon Jan 15, 2022
Victor, it's not clear to me whether this is a bug report or a "how do I do this" question, but in either case if you posted your code along with "I expected X but got Y", it would be easier to understand the issue.