gh-132413: Clear weakref to _datetime after modules are finalized

Lib/test/test_gc.py

@@ -1517,6 +1517,29 @@ def test_ast_fini(self):
         """)
         assert_python_ok("-c", code)
 
+    def test_weakref_to_module_at_shutdown(self):
+        # gh-132413: Weakref gets cleared before modules are finalized
+        code = textwrap.dedent("""
+            import os  # any module other than sys
+
+            def gen():
+                import weakref
+                wr = weakref.ref(os)
+                try:
+                    yield
+                finally:
+                    print(
+                        os is not None,
+                        os is wr()
+                    )
+
+            it = gen()
+            next(it)
+            # quirk: Shutdown starts, then the finally block above follows
+            """)
+        res = assert_python_ok('-c', code)
+        self.assertEqual(res.out.rstrip(), b'True True')
+
 
 def setUpModule():
     global enabled, debug

Misc/NEWS.d/next/Library/2025-06-30-15-12-33.gh-issue-132413.TvpIn2.rst

@@ -0,0 +1 @@
+Fix crash in C version of :mod:`datetime` when used during interpreter shutdown.

Python/pylifecycle.c

@@ -1546,6 +1546,13 @@ static PyObject*
 finalize_remove_modules(PyObject *modules, int verbose)
 {
     PyObject *weaklist = PyList_New(0);
+    PyObject *weak_ext = NULL;  // for extending the weaklist
+    if (weaklist != NULL) {
+        weak_ext = PyList_New(0);
+        if (weak_ext == NULL) {
+            Py_CLEAR(weaklist);
+        }
+    }
     if (weaklist == NULL) {
         PyErr_FormatUnraisable("Exception ignored while removing modules");
     }
@@ -1554,8 +1561,22 @@ finalize_remove_modules(PyObject *modules, int verbose)
         if (weaklist != NULL) { \
             PyObject *wr = PyWeakref_NewRef(mod, NULL); \
             if (wr) { \
-                PyObject *tup = PyTuple_Pack(2, name, wr); \
-                if (!tup || PyList_Append(weaklist, tup) < 0) { \
+                PyObject *list; \
+                PyObject *tup; \
+                if (Py_REFCNT(wr) > 1) { \
+                    /* gh-132413: When the weakref is already used elsewhere,
+                     * finalize_modules_clear_weaklist() rather than the GC
+                     * should clear the referenced module since the GC tries
+                     * to clear the wrakref first.  The weaklist requires the
+                     * order in which such modules are cleared first. */ \
+                    tup = PyTuple_Pack(3, name, wr, mod); \
+                    list = weak_ext; \
+                } \
+                else { \
+                    tup = PyTuple_Pack(2, name, wr); \
+                    list = weaklist; \
+                } \
+                if (!tup || PyList_Append(list, tup) < 0) { \
                     PyErr_FormatUnraisable("Exception ignored while removing modules"); \
                 } \
                 Py_XDECREF(tup); \
@@ -1607,6 +1628,14 @@ finalize_remove_modules(PyObject *modules, int verbose)
             Py_DECREF(iterator);
         }
     }
+
+    if (weaklist != NULL) {
+        if (PyList_Extend(weaklist, weak_ext) < 0) {
+            PyErr_FormatUnraisable("Exception ignored while removing modules");
+        }
+        Py_DECREF(weak_ext);
+    }
+
 #undef CLEAR_MODULE
 #undef STORE_MODULE_WEAKREF