python · vstinner · Feb 21, 2026 · Feb 21, 2026
diff --git a/Lib/test/test_dict.py b/Lib/test/test_dict.py
@@ -1871,6 +1871,35 @@ def test_pickle_iter(self):
                    self.assertEqual(list(unpickled), expected)
                    self.assertEqual(list(it), expected)

+    def test_unhashable_key(self):
+        d = frozendict(a=1)
+        key = [1, 2, 3]
+
+        def check_unhashable_key():
+            msg = "cannot use 'list' as a frozendict key (unhashable type: 'list')"
+            return self.assertRaisesRegex(TypeError, re.escape(msg))
+
+        with check_unhashable_key():
+            key in d
+        with check_unhashable_key():
+            d[key]
+        with check_unhashable_key():
+            d.get(key)
+
+        # Only TypeError exception is overridden,
+        # other exceptions are left unchanged.
+        class HashError:
+            def __hash__(self):
+                raise KeyError('error')
+
+        key2 = HashError()
+        with self.assertRaises(KeyError):
+            key2 in d
+        with self.assertRaises(KeyError):
+            d[key2]
+        with self.assertRaises(KeyError):
+            d.get(key2)
+

 if __name__ == "__main__":
    unittest.main()
@@ -2377,7 +2377,7 @@ PyDict_GetItem(PyObject *op, PyObject *key)
 }

 static void
-dict_unhashable_type(PyObject *key)
+dict_unhashable_type(PyObject *op, PyObject *key)
 {
    PyObject *exc = PyErr_GetRaisedException();
    assert(exc != NULL);
@@ -2386,9 +2386,14 @@ dict_unhashable_type(PyObject *key)
        return;
    }

-    PyErr_Format(PyExc_TypeError,
-                 "cannot use '%T' as a dict key (%S)",
-                 key, exc);
+    const char *errmsg;
+    if (PyObject_IsInstance(op, (PyObject*)&PyFrozenDict_Type)) {
+        errmsg = "cannot use '%T' as a frozendict key (%S)";
+    }
+    else {
+        errmsg = "cannot use '%T' as a dict key (%S)";
+    }
+    PyErr_Format(PyExc_TypeError, errmsg, key, exc);
    Py_DECREF(exc);
 }

@@ -2401,7 +2406,7 @@ _PyDict_LookupIndexAndValue(PyDictObject *mp, PyObject *key, PyObject **value)

    Py_hash_t hash = _PyObject_HashFast(key);
    if (hash == -1) {
-        dict_unhashable_type(key);
+        dict_unhashable_type((PyObject*)mp, key);
        return -1;
    }

@@ -2505,7 +2510,7 @@ PyDict_GetItemRef(PyObject *op, PyObject *key, PyObject **result)

    Py_hash_t hash = _PyObject_HashFast(key);
    if (hash == -1) {
-        dict_unhashable_type(key);
+        dict_unhashable_type(op, key);
        *result = NULL;
        return -1;
    }
@@ -2521,7 +2526,7 @@ _PyDict_GetItemRef_Unicode_LockHeld(PyDictObject *op, PyObject *key, PyObject **

    Py_hash_t hash = _PyObject_HashFast(key);
    if (hash == -1) {
-        dict_unhashable_type(key);
+        dict_unhashable_type((PyObject*)op, key);
        *result = NULL;
        return -1;
    }
@@ -2559,7 +2564,7 @@ PyDict_GetItemWithError(PyObject *op, PyObject *key)
    }
    hash = _PyObject_HashFast(key);
    if (hash == -1) {
-        dict_unhashable_type(key);
+        dict_unhashable_type(op, key);
        return NULL;
    }

@@ -2705,7 +2710,7 @@ setitem_take2_lock_held(PyDictObject *mp, PyObject *key, PyObject *value)

    Py_hash_t hash = _PyObject_HashFast(key);
    if (hash == -1) {
-        dict_unhashable_type(key);
+        dict_unhashable_type((PyObject*)mp, key);
        Py_DECREF(key);
        Py_DECREF(value);
        return -1;
@@ -2864,7 +2869,7 @@ PyDict_DelItem(PyObject *op, PyObject *key)
    assert(key);
    Py_hash_t hash = _PyObject_HashFast(key);
    if (hash == -1) {
-        dict_unhashable_type(key);
+        dict_unhashable_type(op, key);
        return -1;
    }

@@ -3183,7 +3188,7 @@ pop_lock_held(PyObject *op, PyObject *key, PyObject **result)

    Py_hash_t hash = _PyObject_HashFast(key);
    if (hash == -1) {
-        dict_unhashable_type(key);
+        dict_unhashable_type(op, key);
        if (result) {
            *result = NULL;
        }
@@ -3596,7 +3601,7 @@ dict_subscript(PyObject *self, PyObject *key)

    hash = _PyObject_HashFast(key);
    if (hash == -1) {
-        dict_unhashable_type(key);
+        dict_unhashable_type(self, key);
        return NULL;
    }
    ix = _Py_dict_lookup_threadsafe(mp, key, hash, &value);
@@ -4515,7 +4520,7 @@ dict_get_impl(PyDictObject *self, PyObject *key, PyObject *default_value)

    hash = _PyObject_HashFast(key);
    if (hash == -1) {
-        dict_unhashable_type(key);
+        dict_unhashable_type((PyObject*)self, key);
        return NULL;
    }
    ix = _Py_dict_lookup_threadsafe(self, key, hash, &val);
@@ -4547,7 +4552,7 @@ dict_setdefault_ref_lock_held(PyObject *d, PyObject *key, PyObject *default_valu

    hash = _PyObject_HashFast(key);
    if (hash == -1) {
-        dict_unhashable_type(key);
+        dict_unhashable_type(d, key);
        if (result) {
            *result = NULL;
        }
@@ -4990,7 +4995,7 @@ dict_contains(PyObject *op, PyObject *key)
 {
    Py_hash_t hash = _PyObject_HashFast(key);
    if (hash == -1) {
-        dict_unhashable_type(key);
+        dict_unhashable_type(op, key);
        return -1;
    }

@@ -7066,7 +7071,7 @@ _PyDict_SetItem_LockHeld(PyDictObject *dict, PyObject *name, PyObject *value)
    if (value == NULL) {
        Py_hash_t hash = _PyObject_HashFast(name);
        if (hash == -1) {
-            dict_unhashable_type(name);
+            dict_unhashable_type((PyObject*)dict, name);
            return -1;
        }
        return _PyDict_DelItem_KnownHash_LockHeld((PyObject *)dict, name, hash);