From 81f64e385c1733be7c137cceb5fd840dd26f4bf0 Mon Sep 17 00:00:00 2001
From: David Glick <david@glicksoftware.com>
Date: Tue, 27 Aug 2024 09:38:23 -0700
Subject: [PATCH] Fix __weaklistoffset__ in SB_members with
 USE_EXPLICIT_WEAKREFLIST

---
 CHANGES.rst                                         | 3 +++
 src/zope/interface/_zope_interface_coptimizations.c | 4 ++--
 2 files changed, 5 insertions(+), 2 deletions(-)

diff --git a/CHANGES.rst b/CHANGES.rst
index 7243083c..491268b8 100644
--- a/CHANGES.rst
+++ b/CHANGES.rst
@@ -5,6 +5,9 @@
 7.0.3 (unreleased)
 ==================
 
+- Fix `Assertion 'memb->type == T_PYSSIZET' failed.` for Python < 3.12.
+  (`#319 <https://github.com/zopefoundation/zope.interface/issues/319>`_)
+
 
 7.0.2 (2024-08-26)
 ==================
diff --git a/src/zope/interface/_zope_interface_coptimizations.c b/src/zope/interface/_zope_interface_coptimizations.c
index ed7c5a5f..453057a4 100644
--- a/src/zope/interface/_zope_interface_coptimizations.c
+++ b/src/zope/interface/_zope_interface_coptimizations.c
@@ -400,7 +400,7 @@ static PyMemberDef SB_members[] = {
     { "__iro__", T_OBJECT_EX, offsetof(SB, __iro__), 0, "" },
     { "__sro__", T_OBJECT_EX, offsetof(SB, __sro__), 0, "" },
 #if USE_EXPLICIT_WEAKREFLIST
-    { "__weaklistoffset__", T_OBJECT_EX, offsetof(SB, weakreflist), 0, "" },
+    { "__weaklistoffset__", T_PYSSIZET, offsetof(SB, weakreflist), READONLY, "" },
 #endif
     { NULL },
 };
@@ -649,7 +649,7 @@ static PyType_Slot CPB_type_slots[] = {
     {Py_tp_clear,       CPB_clear},
     {Py_tp_dealloc,     CPB_dealloc},
     {Py_tp_members,     CPB_members},
-    /* tp_base cannot be set as a stot -- pass to PyType_FromModuleAndSpec */
+    /* tp_base cannot be set as a slot -- pass to PyType_FromModuleAndSpec */
     {0,                 NULL}
 };