Implement pointer-type creation via __pointer_type__

Author: sergey-miryanov

Lib/ctypes/__init__.py

@@ -266,6 +266,28 @@ class c_bool(_SimpleCData):
 
 from _ctypes import POINTER, pointer, _pointer_type_cache
 
+CType_Type = _Pointer.__base__
+
+def POINTER(cls):
+    if cls is None:
+        return c_void_p
+    try:
+        pt = cls.__pointer_type__
+        if pt is not None:
+            return pt
+    except AttributeError:
+        pass
+    if isinstance(cls, str):
+        return type(f'LP_{cls}', (_Pointer,), {})
+    if issubclass(cls, CType_Type):
+        return type(f'LP_{cls.__name__}', (_Pointer,), {'_type_': cls})
+
+    raise TypeError(f'must be a ctypes-like type: {cls}')
+
+def pointer(arg):
+    typ = POINTER(type(arg))
+    return typ(arg)
+
 class c_wchar_p(_SimpleCData):
     _type_ = "Z"
     def __repr__(self):

Lib/test/test_ctypes/test_c_simple_type_meta.py

@@ -36,7 +36,7 @@ def __new__(cls, name, bases, namespace):
                 else:
                     ptr_bases = (self, POINTER(bases[0]))
                 p = p_meta(f"POINTER({self.__name__})", ptr_bases, {})
-                ctypes._pointer_type_cache[self] = p
+                cls.__pointer_type__ = p
                 return self
 
         class p_meta(PyCSimpleType, ct_meta):
@@ -69,7 +69,7 @@ def __new__(cls, name, bases, namespace):
                 if isinstance(self, p_meta):
                     return self
                 p = p_meta(f"POINTER({self.__name__})", (self, c_void_p), {})
-                ctypes._pointer_type_cache[self] = p
+                cls.__pointer_type__ = p
                 return self
 
         class p_meta(PyCSimpleType, ct_meta):
@@ -103,7 +103,7 @@ def __init__(self, name, bases, namespace):
                 else:
                     ptr_bases = (self, POINTER(bases[0]))
                 p = p_meta(f"POINTER({self.__name__})", ptr_bases, {})
-                ctypes._pointer_type_cache[self] = p
+                type(self).__pointer_type__ = p
 
         class p_meta(PyCSimpleType, ct_meta):
             pass
@@ -135,7 +135,7 @@ def __init__(self, name, bases, namespace):
                 if isinstance(self, p_meta):
                     return
                 p = p_meta(f"POINTER({self.__name__})", (self, c_void_p), {})
-                ctypes._pointer_type_cache[self] = p
+                type(self).__pointer_type__ = p
 
         class p_meta(PyCSimpleType, ct_meta):
             pass

Modules/_ctypes/_ctypes.c

@@ -564,6 +564,21 @@ _ctypes_CType_Type___sizeof___impl(PyObject *self, PyTypeObject *cls)
     return PyLong_FromSsize_t(size);
 }
 
+static PyObject *
+ctype_get_pointer_type(PyObject *self, void *Py_UNUSED(ignored))
+{
+    ctypes_state *st = get_module_state_by_def(Py_TYPE(self));
+    StgInfo *info;
+    if (PyStgInfo_FromType(st, self, &info) < 0) {
+        return NULL;
+    }
+    assert(info); /* Cannot be NULL  */
+    if (info->pointer_type) {
+        return Py_NewRef(info->pointer_type);
+    }
+    Py_RETURN_NONE;
+}
+
 static PyObject *
 CType_Type_repeat(PyObject *self, Py_ssize_t length);
 
@@ -573,12 +588,18 @@ static PyMethodDef ctype_methods[] = {
     {0},
 };
 
+static PyGetSetDef ctype_getsets[] = {
+    { "__pointer_type__", ctype_get_pointer_type, NULL, "pointer type", NULL },
+    { NULL, NULL }
+};
+
 static PyType_Slot ctype_type_slots[] = {
     {Py_tp_token, Py_TP_USE_SPEC},
     {Py_tp_traverse, CType_Type_traverse},
     {Py_tp_clear, CType_Type_clear},
     {Py_tp_dealloc, CType_Type_dealloc},
     {Py_tp_methods, ctype_methods},
+    {Py_tp_getset, ctype_getsets},
     // Sequence protocol.
     {Py_sq_repeat, CType_Type_repeat},
     {0, NULL},
@@ -1174,7 +1195,7 @@ class _ctypes.PyCPointerType "PyObject *" "clinic_state()->PyCPointerType_Type"
 
 
 static int
-PyCPointerType_SetProto(ctypes_state *st, StgInfo *stginfo, PyObject *proto)
+PyCPointerType_SetProto(ctypes_state *st, PyObject *self, StgInfo *stginfo, PyObject *proto)
 {
     if (!proto || !PyType_Check(proto)) {
         PyErr_SetString(PyExc_TypeError,
@@ -1190,8 +1211,17 @@ PyCPointerType_SetProto(ctypes_state *st, StgInfo *stginfo, PyObject *proto)
                         "_type_ must have storage info");
         return -1;
     }
+    if (info->pointer_type) {
+        PyErr_Format(PyExc_TypeError,
+            "pointer type already set: old=%R, new=%R",
+            info->pointer_type, self);
+        return -1;
+    }
+
     Py_INCREF(proto);
     Py_XSETREF(stginfo->proto, proto);
+
+    Py_XSETREF(info->pointer_type, Py_NewRef(self));
     return 0;
 }
 
@@ -1243,7 +1273,7 @@ PyCPointerType_init(PyObject *self, PyObject *args, PyObject *kwds)
     }
     if (proto) {
         const char *current_format;
-        if (PyCPointerType_SetProto(st, stginfo, proto) < 0) {
+        if (PyCPointerType_SetProto(st, self, stginfo, proto) < 0) {
             Py_DECREF(proto);
             return -1;
         }
@@ -1307,7 +1337,7 @@ PyCPointerType_set_type_impl(PyTypeObject *self, PyTypeObject *cls,
         return NULL;
     }
 
-    if (PyCPointerType_SetProto(st, info, type) < 0) {
+    if (PyCPointerType_SetProto(st, (PyObject *)self, info, type) < 0) {
         Py_DECREF(attrdict);
         return NULL;
     }

Modules/_ctypes/callproc.c

@@ -2033,7 +2033,7 @@ create_pointer_type(PyObject *module, PyObject *cls)
     }
 
     if (info) {
-        info->pointer_type = Py_NewRef(result);
+        // info->pointer_type = Py_NewRef(result);
     }
 
     return result;