Two lines of Python that segfault the interpreter
Two lines of Python could crash CPython 3.14 through 3.16 because SETADD assumed it was always operating on a real set, while PEP 749 madeconditionalannotationsrebindable from Python code. The post explains how that assumption broke, why it caused a type-confusion crash, and why stable releases and the development branch needed different fixes.
https://deadlovelll.github.io/2026-08-10-conditional-annotations-set-add-crash/
Timofei Ivankov
Two lines of Python that segfault the interpreter | Timofei Ivankov
SET_ADD trusted the compiler, and PEP 749 quietly handed user code a way to break that trust
1August 19, 2026 102 1
