PL/Python: Fix slicing support for result objects for Python 3

The old way of implementing slicing support by implementing
PySequenceMethods.sq_slice no longer works in Python 3.  You now have
to implement PyMappingMethods.mp_subscript.  Do this by simply
proxying the call to the wrapped list of result dictionaries.
Consolidate some of the subscripting regression tests.

Jan Urbański

src/pl/plpython/expected/plpython_spi.out

---
--- result objects
---
-CREATE FUNCTION test_resultobject_access() RETURNS void
-AS $$
-rv = plpy.execute("SELECT fname, lname, username FROM users ORDER BY username")
-plpy.info([row for row in rv])
-rv[1] = dict([(k, v*2) for (k, v) in rv[1].items()])
-plpy.info([row for row in rv])
-$$ LANGUAGE plpythonu;
-SELECT test_resultobject_access();
-INFO:  [{'lname': 'doe', 'username': 'j_doe', 'fname': 'jane'}, {'lname': 'doe', 'username': 'johnd', 'fname': 'john'}, {'lname': 'smith', 'username': 'slash', 'fname': 'rick'}, {'lname': 'doe', 'username': 'w_doe', 'fname': 'willem'}]
-CONTEXT:  PL/Python function "test_resultobject_access"
-INFO:  [{'lname': 'doe', 'username': 'j_doe', 'fname': 'jane'}, {'lname': 'doedoe', 'username': 'johndjohnd', 'fname': 'johnjohn'}, {'lname': 'smith', 'username': 'slash', 'fname': 'rick'}, {'lname': 'doe', 'username': 'w_doe', 'fname': 'willem'}]
-CONTEXT:  PL/Python function "test_resultobject_access"
- test_resultobject_access 
---------------------------
- 
-(1 row)
-
 --
 -- nested calls
 --
@@ -228,6 +208,61 @@ SELECT result_len_test($$UPDATE foo3 SET b= '' WHERE a = 2$$);
                0
 (1 row)
 
+CREATE FUNCTION result_subscript_test() RETURNS void
+AS $$
+result = plpy.execute("SELECT 1 AS c UNION SELECT 2 "
+                      "UNION SELECT 3 UNION SELECT 4")
+
+plpy.info(result[1]['c'])
+plpy.info(result[-1]['c'])
+
+plpy.info([item['c'] for item in result[1:3]])
+plpy.info([item['c'] for item in result[::2]])
+
+result[-1] = {'c': 1000}
+result[:2] = [{'c': 10}, {'c': 100}]
+plpy.info([item['c'] for item in result[:]])
+
+# raises TypeError, but the message differs on Python 2.6, so silence it
+try:
+    plpy.info(result['foo'])
+except TypeError:
+    pass
+else:
+    assert False, "TypeError not raised"
+
+$$ LANGUAGE plpythonu;
+SELECT result_subscript_test();
+INFO:  2
+CONTEXT:  PL/Python function "result_subscript_test"
+INFO:  4
+CONTEXT:  PL/Python function "result_subscript_test"
+INFO:  [2, 3]
+CONTEXT:  PL/Python function "result_subscript_test"
+INFO:  [1, 3]
+CONTEXT:  PL/Python function "result_subscript_test"
+INFO:  [10, 100, 3, 1000]
+CONTEXT:  PL/Python function "result_subscript_test"
+ result_subscript_test 
+-----------------------
+ 
+(1 row)
+
+CREATE FUNCTION result_empty_test() RETURNS void
+AS $$
+result = plpy.execute("select 1 where false")
+
+plpy.info(result[:])
+
+$$ LANGUAGE plpythonu;
+SELECT result_empty_test();
+INFO:  []
+CONTEXT:  PL/Python function "result_empty_test"
+ result_empty_test 
+-------------------
+ 
+(1 row)
+
 -- cursor objects
 CREATE FUNCTION simple_cursor_test() RETURNS int AS $$
 res = plpy.cursor("select fname, lname from users")

src/pl/plpython/plpy_resultobject.c

@@ -23,6 +23,8 @@ static PyObject *PLy_result_item(PyObject *arg, Py_ssize_t idx);
 static PyObject *PLy_result_slice(PyObject *arg, Py_ssize_t lidx, Py_ssize_t hidx);
 static int	PLy_result_ass_item(PyObject *arg, Py_ssize_t idx, PyObject *item);
 static int	PLy_result_ass_slice(PyObject *rg, Py_ssize_t lidx, Py_ssize_t hidx, PyObject *slice);
+static PyObject *PLy_result_subscript(PyObject *arg, PyObject *item);
+static int PLy_result_ass_subscript(PyObject* self, PyObject* item, PyObject* value);
 
 static char PLy_result_doc[] = {
 	"Results of a PostgreSQL query"
@@ -38,6 +40,12 @@ static PySequenceMethods PLy_result_as_sequence = {
 	PLy_result_ass_slice,		/* sq_ass_slice */
 };
 
+static PyMappingMethods PLy_result_as_mapping = {
+	PLy_result_length,			/* mp_length */
+	PLy_result_subscript,		/* mp_subscript */
+	PLy_result_ass_subscript,	/* mp_ass_subscript */
+};
+
 static PyMethodDef PLy_result_methods[] = {
 	{"colnames", PLy_result_colnames, METH_NOARGS, NULL},
 	{"coltypes", PLy_result_coltypes, METH_NOARGS, NULL},
@@ -64,7 +72,7 @@ static PyTypeObject PLy_ResultType = {
 	0,							/* tp_repr */
 	0,							/* tp_as_number */
 	&PLy_result_as_sequence,	/* tp_as_sequence */
-	0,							/* tp_as_mapping */
+	&PLy_result_as_mapping,		/* tp_as_mapping */
 	0,							/* tp_hash */
 	0,							/* tp_call */
 	0,							/* tp_str */
@@ -251,3 +259,19 @@ PLy_result_ass_slice(PyObject *arg, Py_ssize_t lidx, Py_ssize_t hidx, PyObject *
 	rv = PyList_SetSlice(ob->rows, lidx, hidx, slice);
 	return rv;
 }
+
+static PyObject *
+PLy_result_subscript(PyObject *arg, PyObject *item)
+{
+	PLyResultObject	*ob = (PLyResultObject *) arg;
+
+	return PyObject_GetItem(ob->rows, item);
+}
+
+static int
+PLy_result_ass_subscript(PyObject *arg, PyObject *item, PyObject *value)
+{
+	PLyResultObject	*ob = (PLyResultObject *) arg;
+
+	return PyObject_SetItem(ob->rows, item, value);
+}

src/pl/plpython/sql/plpython_spi.sql

---
--- result objects
---
-
-CREATE FUNCTION test_resultobject_access() RETURNS void
-AS $$
-rv = plpy.execute("SELECT fname, lname, username FROM users ORDER BY username")
-plpy.info([row for row in rv])
-rv[1] = dict([(k, v*2) for (k, v) in rv[1].items()])
-plpy.info([row for row in rv])
-$$ LANGUAGE plpythonu;
-
-SELECT test_resultobject_access();
-
-
 --
 -- nested calls
 --
@@ -147,6 +132,42 @@ SELECT result_len_test($$CREATE TEMPORARY TABLE foo3 (a int, b text)$$);
 SELECT result_len_test($$INSERT INTO foo3 VALUES (1, 'one'), (2, 'two')$$);
 SELECT result_len_test($$UPDATE foo3 SET b= '' WHERE a = 2$$);
 
+CREATE FUNCTION result_subscript_test() RETURNS void
+AS $$
+result = plpy.execute("SELECT 1 AS c UNION SELECT 2 "
+                      "UNION SELECT 3 UNION SELECT 4")
+
+plpy.info(result[1]['c'])
+plpy.info(result[-1]['c'])
+
+plpy.info([item['c'] for item in result[1:3]])
+plpy.info([item['c'] for item in result[::2]])
+
+result[-1] = {'c': 1000}
+result[:2] = [{'c': 10}, {'c': 100}]
+plpy.info([item['c'] for item in result[:]])
+
+# raises TypeError, but the message differs on Python 2.6, so silence it
+try:
+    plpy.info(result['foo'])
+except TypeError:
+    pass
+else:
+    assert False, "TypeError not raised"
+
+$$ LANGUAGE plpythonu;
+
+SELECT result_subscript_test();
+
+CREATE FUNCTION result_empty_test() RETURNS void
+AS $$
+result = plpy.execute("select 1 where false")
+
+plpy.info(result[:])
+
+$$ LANGUAGE plpythonu;
+
+SELECT result_empty_test();
 
 -- cursor objects