Prepare for Python "Limited API" in PL/Python

Using the Python Limited API would allow building PL/Python against
any Python 3.x version and using another Python 3.x version at run
time.  This commit does not activate that, but it prepares the code to
only use APIs supported by the Limited API.

Implementation details:

- Convert static types to heap types
  (https://docs.python.org/3/howto/isolating-extensions.html#heap-types).

- Replace PyRun_String() with component functions.

- Replace PyList_SET_ITEM() with PyList_SetItem().

Reviewed-by: Jakob Egger <jakob@eggerapps.at>
Discussion: https://www.postgresql.org/message-id/flat/ee410de1-1e0b-4770-b125-eeefd4726a24@eisentraut.org

1 files changed, 60 insertions, 38 deletions

diff --git a/src/pl/plpython/plpy_resultobject.c b/src/pl/plpython/plpy_resultobject.c
index 95acce65493..f2628205669 100644
--- a/src/pl/plpython/plpy_resultobject.c
+++ b/src/pl/plpython/plpy_resultobject.c
@@ -10,7 +10,7 @@
 #include "plpy_resultobject.h"
 #include "plpython.h"
 
-static void PLy_result_dealloc(PyObject *arg);
+static void PLy_result_dealloc(PLyResultObject *self);
 static PyObject *PLy_result_colnames(PyObject *self, PyObject *unused);
 static PyObject *PLy_result_coltypes(PyObject *self, PyObject *unused);
 static PyObject *PLy_result_coltypmods(PyObject *self, PyObject *unused);
@@ -24,17 +24,6 @@ static int	PLy_result_ass_subscript(PyObject *arg, PyObject *item, PyObject *val
 
 static char PLy_result_doc[] = "Results of a PostgreSQL query";
 
-static PySequenceMethods PLy_result_as_sequence = {
-	.sq_length = PLy_result_length,
-	.sq_item = PLy_result_item,
-};
-
-static PyMappingMethods PLy_result_as_mapping = {
-	.mp_length = PLy_result_length,
-	.mp_subscript = PLy_result_subscript,
-	.mp_ass_subscript = PLy_result_ass_subscript,
-};
-
 static PyMethodDef PLy_result_methods[] = {
 	{"colnames", PLy_result_colnames, METH_NOARGS, NULL},
 	{"coltypes", PLy_result_coltypes, METH_NOARGS, NULL},
@@ -44,23 +33,55 @@ static PyMethodDef PLy_result_methods[] = {
 	{NULL, NULL, 0, NULL}
 };
 
-static PyTypeObject PLy_ResultType = {
-	PyVarObject_HEAD_INIT(NULL, 0)
-	.tp_name = "PLyResult",
-	.tp_basicsize = sizeof(PLyResultObject),
-	.tp_dealloc = PLy_result_dealloc,
-	.tp_as_sequence = &PLy_result_as_sequence,
-	.tp_as_mapping = &PLy_result_as_mapping,
-	.tp_str = &PLy_result_str,
-	.tp_flags = Py_TPFLAGS_DEFAULT | Py_TPFLAGS_BASETYPE,
-	.tp_doc = PLy_result_doc,
-	.tp_methods = PLy_result_methods,
+static PyType_Slot PLyResult_slots[] =
+{
+	{
+		Py_tp_dealloc, PLy_result_dealloc
+	},
+	{
+		Py_sq_length, PLy_result_length
+	},
+	{
+		Py_sq_item, PLy_result_item
+	},
+	{
+		Py_mp_length, PLy_result_length
+	},
+	{
+		Py_mp_subscript, PLy_result_subscript
+	},
+	{
+		Py_mp_ass_subscript, PLy_result_ass_subscript
+	},
+	{
+		Py_tp_str, PLy_result_str
+	},
+	{
+		Py_tp_doc, (char *) PLy_result_doc
+	},
+	{
+		Py_tp_methods, PLy_result_methods
+	},
+	{
+		0, NULL
+	}
 };
 
+static PyType_Spec PLyResult_spec =
+{
+	.name = "PLyResult",
+		.basicsize = sizeof(PLyResultObject),
+		.flags = Py_TPFLAGS_DEFAULT | Py_TPFLAGS_BASETYPE,
+		.slots = PLyResult_slots,
+};
+
+static PyTypeObject *PLy_ResultType;
+
 void
 PLy_result_init_type(void)
 {
-	if (PyType_Ready(&PLy_ResultType) < 0)
+	PLy_ResultType = (PyTypeObject *) PyType_FromSpec(&PLyResult_spec);
+	if (!PLy_ResultType)
 		elog(ERROR, "could not initialize PLy_ResultType");
 }
 
@@ -69,7 +90,7 @@ PLy_result_new(void)
 {
 	PLyResultObject *ob;
 
-	if ((ob = PyObject_New(PLyResultObject, &PLy_ResultType)) == NULL)
+	if ((ob = PyObject_New(PLyResultObject, PLy_ResultType)) == NULL)
 		return NULL;
 
 	/* ob->tuples = NULL; */
@@ -89,20 +110,21 @@ PLy_result_new(void)
 }
 
 static void
-PLy_result_dealloc(PyObject *arg)
+PLy_result_dealloc(PLyResultObject *self)
 {
-	PLyResultObject *ob = (PLyResultObject *) arg;
+	PyTypeObject *tp = Py_TYPE(self);
 
-	Py_XDECREF(ob->nrows);
-	Py_XDECREF(ob->rows);
-	Py_XDECREF(ob->status);
-	if (ob->tupdesc)
+	Py_XDECREF(self->nrows);
+	Py_XDECREF(self->rows);
+	Py_XDECREF(self->status);
+	if (self->tupdesc)
 	{
-		FreeTupleDesc(ob->tupdesc);
-		ob->tupdesc = NULL;
+		FreeTupleDesc(self->tupdesc);
+		self->tupdesc = NULL;
 	}
 
-	arg->ob_type->tp_free(arg);
+	PyObject_Free(self);
+	Py_DECREF(tp);
 }
 
 static PyObject *
@@ -125,7 +147,7 @@ PLy_result_colnames(PyObject *self, PyObject *unused)
 	{
 		Form_pg_attribute attr = TupleDescAttr(ob->tupdesc, i);
 
-		PyList_SET_ITEM(list, i, PLyUnicode_FromString(NameStr(attr->attname)));
+		PyList_SetItem(list, i, PLyUnicode_FromString(NameStr(attr->attname)));
 	}
 
 	return list;
@@ -151,7 +173,7 @@ PLy_result_coltypes(PyObject *self, PyObject *unused)
 	{
 		Form_pg_attribute attr = TupleDescAttr(ob->tupdesc, i);
 
-		PyList_SET_ITEM(list, i, PyLong_FromLong(attr->atttypid));
+		PyList_SetItem(list, i, PyLong_FromLong(attr->atttypid));
 	}
 
 	return list;
@@ -177,7 +199,7 @@ PLy_result_coltypmods(PyObject *self, PyObject *unused)
 	{
 		Form_pg_attribute attr = TupleDescAttr(ob->tupdesc, i);
 
-		PyList_SET_ITEM(list, i, PyLong_FromLong(attr->atttypmod));
+		PyList_SetItem(list, i, PyLong_FromLong(attr->atttypmod));
 	}
 
 	return list;
@@ -227,7 +249,7 @@ PLy_result_str(PyObject *arg)
 	PLyResultObject *ob = (PLyResultObject *) arg;
 
 	return PyUnicode_FromFormat("<%s status=%S nrows=%S rows=%S>",
-								Py_TYPE(ob)->tp_name,
+								"PLyResult",
 								ob->status,
 								ob->nrows,
 								ob->rows);