PL/Python: Add result object str handler

This is intended so that say plpy.debug(rv) prints something useful for
debugging query execution results.

reviewed by Steve Singer

doc/src/sgml/plpython.sgml

@@ -956,6 +956,17 @@ foo = rv[i]["my_column"]
          </para>
         </listitem>
        </varlistentry>
+
+       <varlistentry>
+        <term><literal><function>__str__</function>()</literal></term>
+        <listitem>
+         <para>
+          The standard <literal>__str__</literal> method is defined so that it
+          is possible for example to debug query execution results
+          using <literal>plpy.debug(rv)</literal>.
+         </para>
+        </listitem>
+       </varlistentry>
       </variablelist>
      </para>
 

src/pl/plpython/expected/plpython_spi.out

@@ -263,6 +263,24 @@ CONTEXT:  PL/Python function "result_empty_test"
  
 (1 row)
 
+CREATE FUNCTION result_str_test(cmd text) RETURNS text
+AS $$
+plan = plpy.prepare(cmd)
+result = plpy.execute(plan)
+return str(result)
+$$ LANGUAGE plpythonu;
+SELECT result_str_test($$SELECT 1 AS foo, '11'::text AS bar UNION SELECT 2, '22'$$);
+                                   result_str_test                                    
+--------------------------------------------------------------------------------------
+ <PLyResult status=5 nrows=2 rows=[{'foo': 1, 'bar': '11'}, {'foo': 2, 'bar': '22'}]>
+(1 row)
+
+SELECT result_str_test($$CREATE TEMPORARY TABLE foo1 (a int, b text)$$);
+           result_str_test            
+--------------------------------------
+ <PLyResult status=4 nrows=0 rows=[]>
+(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

@@ -22,6 +22,7 @@ static Py_ssize_t PLy_result_length(PyObject *arg);
 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_slice(PyObject *arg, Py_ssize_t lidx, Py_ssize_t hidx, PyObject *slice);
+static PyObject *PLy_result_str(PyObject *arg);
 static PyObject *PLy_result_subscript(PyObject *arg, PyObject *item);
 static int	PLy_result_ass_subscript(PyObject *self, PyObject *item, PyObject *value);
 
@@ -74,7 +75,7 @@ static PyTypeObject PLy_ResultType = {
 	&PLy_result_as_mapping,		/* tp_as_mapping */
 	0,							/* tp_hash */
 	0,							/* tp_call */
-	0,							/* tp_str */
+	&PLy_result_str,			/* tp_str */
 	0,							/* tp_getattro */
 	0,							/* tp_setattro */
 	0,							/* tp_as_buffer */
@@ -248,6 +249,26 @@ PLy_result_ass_slice(PyObject *arg, Py_ssize_t lidx, Py_ssize_t hidx, PyObject *
 	return rv;
 }
 
+static PyObject *
+PLy_result_str(PyObject *arg)
+{
+	PLyResultObject *ob = (PLyResultObject *) arg;
+
+#if PY_MAJOR_VERSION >= 3
+	return PyUnicode_FromFormat("<%s status=%S nrows=%S rows=%S>",
+								Py_TYPE(ob)->tp_name,
+								ob->status,
+								ob->nrows,
+								ob->rows);
+#else
+	return PyString_FromFormat("<%s status=%ld nrows=%ld rows=%s>",
+							   ob->ob_type->tp_name,
+							   PyInt_AsLong(ob->status),
+							   PyInt_AsLong(ob->nrows),
+							   PyString_AsString(PyObject_Str(ob->rows)));
+#endif
+}
+
 static PyObject *
 PLy_result_subscript(PyObject *arg, PyObject *item)
 {

src/pl/plpython/sql/plpython_spi.sql

@@ -169,6 +169,16 @@ $$ LANGUAGE plpythonu;
 
 SELECT result_empty_test();
 
+CREATE FUNCTION result_str_test(cmd text) RETURNS text
+AS $$
+plan = plpy.prepare(cmd)
+result = plpy.execute(plan)
+return str(result)
+$$ LANGUAGE plpythonu;
+
+SELECT result_str_test($$SELECT 1 AS foo, '11'::text AS bar UNION SELECT 2, '22'$$);
+SELECT result_str_test($$CREATE TEMPORARY TABLE foo1 (a int, b text)$$);
+
 -- cursor objects
 
 CREATE FUNCTION simple_cursor_test() RETURNS int AS $$