Issue 2235: __hash__ is once again inherited by default, but inheritance can be blocked explicitly so that collections.Hashable remains meaningful
diff --git a/Objects/typeobject.c b/Objects/typeobject.c
index e0ae55b..0af3f30 100644
--- a/Objects/typeobject.c
+++ b/Objects/typeobject.c
@@ -3648,27 +3648,6 @@
type->tp_flags |= Py_TPFLAGS_DICT_SUBCLASS;
}
-static char *hash_name_op[] = {
- "__eq__",
- "__cmp__",
- "__hash__",
- NULL
-};
-
-static int
-overrides_hash(PyTypeObject *type)
-{
- char **p;
- PyObject *dict = type->tp_dict;
-
- assert(dict != NULL);
- for (p = hash_name_op; *p; p++) {
- if (PyDict_GetItemString(dict, *p) != NULL)
- return 1;
- }
- return 0;
-}
-
static void
inherit_slots(PyTypeObject *type, PyTypeObject *base)
{
@@ -3802,8 +3781,7 @@
if (type->tp_flags & base->tp_flags & Py_TPFLAGS_HAVE_RICHCOMPARE) {
if (type->tp_compare == NULL &&
type->tp_richcompare == NULL &&
- type->tp_hash == NULL &&
- !overrides_hash(type))
+ type->tp_hash == NULL)
{
type->tp_compare = base->tp_compare;
type->tp_richcompare = base->tp_richcompare;
@@ -3984,18 +3962,6 @@
}
}
- /* Hack for tp_hash and __hash__.
- If after all that, tp_hash is still NULL, and __hash__ is not in
- tp_dict, set tp_dict['__hash__'] equal to None.
- This signals that __hash__ is not inherited.
- */
- if (type->tp_hash == NULL &&
- PyDict_GetItemString(type->tp_dict, "__hash__") == NULL &&
- PyDict_SetItemString(type->tp_dict, "__hash__", Py_None) < 0)
- {
- goto error;
- }
-
/* Some more special stuff */
base = type->tp_base;
if (base != NULL) {
@@ -5280,10 +5246,8 @@
func = lookup_method(self, "__cmp__", &cmp_str);
}
if (func != NULL) {
- PyErr_Format(PyExc_TypeError, "unhashable type: '%.200s'",
- self->ob_type->tp_name);
Py_DECREF(func);
- return -1;
+ return PyObject_HashNotImplemented(self);
}
PyErr_Clear();
h = _Py_HashPointer((void *)self);
@@ -6034,6 +5998,13 @@
sanity checks. I'll buy the first person to
point out a bug in this reasoning a beer. */
}
+ else if (descr == Py_None &&
+ strcmp(p->name, "__hash__") == 0) {
+ /* We specifically allow __hash__ to be set to None
+ to prevent inheritance of the default
+ implementation from object.__hash__ */
+ specific = PyObject_HashNotImplemented;
+ }
else {
use_generic = 1;
generic = p->function;
@@ -6247,12 +6218,21 @@
continue;
if (PyDict_GetItem(dict, p->name_strobj))
continue;
- descr = PyDescr_NewWrapper(type, p, *ptr);
- if (descr == NULL)
- return -1;
- if (PyDict_SetItem(dict, p->name_strobj, descr) < 0)
- return -1;
- Py_DECREF(descr);
+ if (*ptr == PyObject_HashNotImplemented) {
+ /* Classes may prevent the inheritance of the tp_hash
+ slot by storing PyObject_HashNotImplemented in it. Make it
+ visible as a None value for the __hash__ attribute. */
+ if (PyDict_SetItem(dict, p->name_strobj, Py_None) < 0)
+ return -1;
+ }
+ else {
+ descr = PyDescr_NewWrapper(type, p, *ptr);
+ if (descr == NULL)
+ return -1;
+ if (PyDict_SetItem(dict, p->name_strobj, descr) < 0)
+ return -1;
+ Py_DECREF(descr);
+ }
}
if (type->tp_new != NULL) {
if (add_tp_new_wrapper(type) < 0)