Issue #11241: subclasses of ctypes.Array can now be subclassed.

Lib/ctypes/test/test_arrays.py

@@ -127,5 +127,57 @@ class my_int(c_int):
         t2 = my_int * 1
         self.assertTrue(t1 is t2)
 
+    def test_subclass(self):
+        class T(Array):
+            _type_ = c_int
+            _length_ = 13
+        class U(T):
+            pass
+        class V(U):
+            pass
+        class W(V):
+            pass
+        class X(T):
+            _type_ = c_short
+        class Y(T):
+            _length_ = 187
+
+        for c in [T, U, V, W]:
+            self.assertEqual(c._type_, c_int)
+            self.assertEqual(c._length_, 13)
+            self.assertEqual(c()._type_, c_int)
+            self.assertEqual(c()._length_, 13)
+
+        self.assertEqual(X._type_, c_short)
+        self.assertEqual(X._length_, 13)
+        self.assertEqual(X()._type_, c_short)
+        self.assertEqual(X()._length_, 13)
+
+        self.assertEqual(Y._type_, c_int)
+        self.assertEqual(Y._length_, 187)
+        self.assertEqual(Y()._type_, c_int)
+        self.assertEqual(Y()._length_, 187)
+
+    def test_bad_subclass(self):
+        import sys
+
+        with self.assertRaises(AttributeError):
+            class T(Array):
+                pass
+        with self.assertRaises(AttributeError):
+            class T(Array):
+                _type_ = c_int
+        with self.assertRaises(AttributeError):
+            class T(Array):
+                _length_ = 13
+        with self.assertRaises(OverflowError):
+            class T(Array):
+                _type_ = c_int
+                _length_ = sys.maxsize * 2
+        with self.assertRaises(AttributeError):
+            class T(Array):
+                _type_ = c_int
+                _length_ = 1.87
+
 if __name__ == '__main__':
     unittest.main()

Misc/NEWS

@@ -185,6 +185,8 @@ Library
 Extension Modules
 -----------------
 
+- Issue #11241: subclasses of ctypes.Array can now be subclassed.
+
 - Issue #9651: Fix a crash when ctypes.create_string_buffer(0) was passed to
   some functions like file.write().
 

Modules/_ctypes/_ctypes.c

@@ -1256,49 +1256,57 @@ PyCArrayType_new(PyTypeObject *type, PyObject *args, PyObject *kwds)
     PyTypeObject *result;
     StgDictObject *stgdict;
     StgDictObject *itemdict;
-    PyObject *proto;
-    PyObject *typedict;
+    PyObject *length_attr, *type_attr;
     long length;
     int overflow;
     Py_ssize_t itemsize, itemalign;
     char buf[32];
 
-    typedict = PyTuple_GetItem(args, 2);
-    if (!typedict)
+    /* create the new instance (which is a class,
+       since we are a metatype!) */
+    result = (PyTypeObject *)PyType_Type.tp_new(type, args, kwds);
+    if (result == NULL)
         return NULL;
 
-    proto = PyDict_GetItemString(typedict, "_length_"); /* Borrowed ref */
-    if (!proto || !PyLong_Check(proto)) {
+    /* Initialize these variables to NULL so that we can simplify error
+       handling by using Py_XDECREF.  */
+    stgdict = NULL;
+    type_attr = NULL;
+
+    length_attr = PyObject_GetAttrString((PyObject *)result, "_length_");
+    if (!length_attr || !PyLong_Check(length_attr)) {
         PyErr_SetString(PyExc_AttributeError,
                         "class must define a '_length_' attribute, "
                         "which must be a positive integer");
-        return NULL;
+        Py_XDECREF(length_attr);
+        goto error;
     }
-    length = PyLong_AsLongAndOverflow(proto, &overflow);
+    length = PyLong_AsLongAndOverflow(length_attr, &overflow);
     if (overflow) {
         PyErr_SetString(PyExc_OverflowError,
                         "The '_length_' attribute is too large");
-        return NULL;
+        Py_DECREF(length_attr);
+        goto error;
     }
+    Py_DECREF(length_attr);
 
-    proto = PyDict_GetItemString(typedict, "_type_"); /* Borrowed ref */
-    if (!proto) {
+    type_attr = PyObject_GetAttrString((PyObject *)result, "_type_");
+    if (!type_attr) {
         PyErr_SetString(PyExc_AttributeError,
                         "class must define a '_type_' attribute");
-        return NULL;
+        goto error;
     }
 
     stgdict = (StgDictObject *)PyObject_CallObject(
         (PyObject *)&PyCStgDict_Type, NULL);
     if (!stgdict)
-        return NULL;
+        goto error;
 
-    itemdict = PyType_stgdict(proto);
+    itemdict = PyType_stgdict(type_attr);
     if (!itemdict) {
         PyErr_SetString(PyExc_TypeError,
                         "_type_ must have storage info");
-        Py_DECREF((PyObject *)stgdict);
-        return NULL;
+        goto error;
     }
 
     assert(itemdict->format);
@@ -1309,16 +1317,12 @@ PyCArrayType_new(PyTypeObject *type, PyObject *args, PyObject *kwds)
         sprintf(buf, "(%ld)", length);
         stgdict->format = _ctypes_alloc_format_string(buf, itemdict->format);
     }
-    if (stgdict->format == NULL) {
-        Py_DECREF((PyObject *)stgdict);
-        return NULL;
-    }
+    if (stgdict->format == NULL)
+        goto error;
     stgdict->ndim = itemdict->ndim + 1;
     stgdict->shape = PyMem_Malloc(sizeof(Py_ssize_t *) * stgdict->ndim);
-    if (stgdict->shape == NULL) {
-        Py_DECREF((PyObject *)stgdict);
-        return NULL;
-    }
+    if (stgdict->shape == NULL)
+        goto error;
     stgdict->shape[0] = length;
     memmove(&stgdict->shape[1], itemdict->shape,
         sizeof(Py_ssize_t) * (stgdict->ndim - 1));
@@ -1327,7 +1331,7 @@ PyCArrayType_new(PyTypeObject *type, PyObject *args, PyObject *kwds)
     if (length * itemsize < 0) {
         PyErr_SetString(PyExc_OverflowError,
                         "array too large");
-        return NULL;
+        goto error;
     }
 
     itemalign = itemdict->align;
@@ -1338,26 +1342,16 @@ PyCArrayType_new(PyTypeObject *type, PyObject *args, PyObject *kwds)
     stgdict->size = itemsize * length;
     stgdict->align = itemalign;
     stgdict->length = length;
-    Py_INCREF(proto);
-    stgdict->proto = proto;
+    stgdict->proto = type_attr;
 
     stgdict->paramfunc = &PyCArrayType_paramfunc;
 
     /* Arrays are passed as pointers to function calls. */
     stgdict->ffi_type_pointer = ffi_type_pointer;
 
-    /* create the new instance (which is a class,
-       since we are a metatype!) */
-    result = (PyTypeObject *)PyType_Type.tp_new(type, args, kwds);
-    if (result == NULL)
-        return NULL;
-
     /* replace the class dict by our updated spam dict */
-    if (-1 == PyDict_Update((PyObject *)stgdict, result->tp_dict)) {
-        Py_DECREF(result);
-        Py_DECREF((PyObject *)stgdict);
-        return NULL;
-    }
+    if (-1 == PyDict_Update((PyObject *)stgdict, result->tp_dict))
+        goto error;
     Py_DECREF(result->tp_dict);
     result->tp_dict = (PyObject *)stgdict;
 
@@ -1366,15 +1360,20 @@ PyCArrayType_new(PyTypeObject *type, PyObject *args, PyObject *kwds)
     */
     if (itemdict->getfunc == _ctypes_get_fielddesc("c")->getfunc) {
         if (-1 == add_getset(result, CharArray_getsets))
-            return NULL;
+            goto error;
 #ifdef CTYPES_UNICODE
     } else if (itemdict->getfunc == _ctypes_get_fielddesc("u")->getfunc) {
         if (-1 == add_getset(result, WCharArray_getsets))
-            return NULL;
+            goto error;
 #endif
     }
 
     return (PyObject *)result;
+error:
+    Py_XDECREF((PyObject*)stgdict);
+    Py_XDECREF(type_attr);
+    Py_DECREF(result);
+    return NULL;
 }
 
 PyTypeObject PyCArrayType_Type = {