What happened?

NULL pointer dereference in the _datetime C module → SIGSEGV. Reproducer:

import sys, gc
import _datetime

td = _datetime.timedelta            # static C type, survives the module
del sys.modules['_datetime']
del _datetime
sys.modules['_datetime'] = None     # block re-import
gc.collect()                        # module object is collected

td(seconds=2)                       # -> Segmentation fault

gdb at the crash: st == (datetime_state *) 0x0, with an ImportError already pending.

Root cause

The datetime types are static and can outlive the module, so per-module state (gh-117398) is fetched via _get_current_state(), which can return NULL when the module weakref is dead and re-import fails (blocked in sys.modules):

Callers dereference the returned state without a NULL check. At the crash site CONST_US_PER_SECOND(st) is st->us_per_second, so st == NULL → NULL deref:

Originally hit via ./python -X lazy_imports=all -m test test_datetime (segfault in test_strptime; test_datetime is also listed in #149640).

Versions

• CPython main (3.16.0a0, ab930175e7e). Present since 3.14 (Isolate the _datetime extension module #117398) → 3.14, 3.15, main. Linux.
• Build: CC=/opt/llvm/bin/clang CXX=/opt/llvm/bin/clang++ LDFLAGS='-fuse-ld=lld' ./configure; clang/lld 23.0.0git (4695c84).

Linked PRs

• gh-151039: Fix a crash when datetime.timedelta outlives _datetime module #151044