[New-bugs-announce] [issue45266] subtype_clear can not be called from derived types
Victor Milovanov
report at bugs.python.org
Wed Sep 22 15:16:19 EDT 2021
New submission from Victor Milovanov <lostfreeman at gmail.com>:
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:
1) it does not perform the usual cleanup, because in this code
base = type;
while ((baseclear = base->tp_clear) == subtype_clear)
the loop condition is immediately false, as my types overrode tp_clear
2) later on it calls baseclear on the same object. But because of the loop above baseclear actually points to my type's custom tp_clear implementation, which leads to reentry to that function (basically a stack overflow, unless there's a guard against it).
----------
components: C API
messages: 402466
nosy: Victor Milovanov
priority: normal
severity: normal
status: open
title: subtype_clear can not be called from derived types
type: behavior
versions: Python 3.10, Python 3.11, Python 3.6, Python 3.7, Python 3.8, Python 3.9
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Python tracker <report at bugs.python.org>
<https://bugs.python.org/issue45266>
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