Crash when deleting decimal.Context.rounding through the descriptor

Crash report

What happened?

import decimal
decimal.Context.rounding.__delete__(decimal.Context())

Segmentation fault (core dumped)

context_setround() passes the value to getround(), which calls
PyUnicode_Check() on it without checking it for NULL, and the setter is
called with NULL when the attribute is deleted. Plain del ctx.rounding is
safe, because context_setattr() rejects deletion — but it is bypassed by
calling the descriptor.

The other five Context getsets do not crash, but raise SystemError:

import decimal
decimal.Context.prec.__delete__(decimal.Context())
# SystemError: ../Objects/longobject.c:577: bad argument to internal function

Same for Emin, Emax, capitals and clamp.

CPython versions tested on:

3.15, 3.14, 3.13, 3.12

Operating systems tested on:

Windows

Output from running 'python -VV' on the command line:

Python 3.12.3 (main, Jan 8 2026, 11:30:50) [GCC 13.3.0] / Python 3.14.2 (main, Dec 17 2025, 21:10:36) [MSC v.1944 64 bit (AMD64)]

Linked PRs

• gh-156807

decimal.Context.rounding.delete から始め、context_setround()、getround()、context_setattr() を通る descriptor の経路を追跡します。rounding、prec、Emin、Emax、capitals、clamp の削除時の動作を比較します。完了とは、descriptor の削除によってクラッシュしたり、意図しない SystemError が発生したりしなくなることです。リンクされている PR gh-156807 は、作業がすでに進行中であることを示しています。