bpo-43908: Make array.array type immutable (GH-25696)

Co-authored-by: Victor Stinner <[email protected]>

Author: Erlend Egeberg Aasland

Lib/test/test_array.py

@@ -40,6 +40,12 @@ def test_bad_constructor(self):
         self.assertRaises(TypeError, array.array, 'xx')
         self.assertRaises(ValueError, array.array, 'x')
 
+    @support.cpython_only
+    def test_immutable(self):
+        # bpo-43908: check that array.array is immutable
+        with self.assertRaises(TypeError):
+            array.array.foo = 1
+
     def test_empty(self):
         # Exercise code for handling zero-length arrays
         a = array.array('B')

Misc/NEWS.d/next/Core and Builtins/2021-04-26-20-59-17.bpo-43908.-COW4-.rst

@@ -0,0 +1,2 @@
+Make the :class:`array.array` type immutable. Patch by
+Erlend E. Aasland.

Modules/arraymodule.c

@@ -2847,7 +2847,8 @@ static PyType_Slot array_slots[] = {
 static PyType_Spec array_spec = {
     .name = "array.array",
     .basicsize = sizeof(arrayobject),
-    .flags = Py_TPFLAGS_DEFAULT | Py_TPFLAGS_BASETYPE,
+    .flags = (Py_TPFLAGS_DEFAULT | Py_TPFLAGS_BASETYPE |
+              Py_TPFLAGS_IMMUTABLETYPE),
     .slots = array_slots,
 };