python: Add a Caps.get_value variant that does not copy the structures

Keeping the __getitem__ implementation the same way

This also now make structure.set_value() raise an exception if the structure
was not writable

Part-of: <https://gitlab.freedesktop.org/gstreamer/gstreamer/-/merge_requests/9027>

subprojects/gst-python/gi/overrides/Gst.py

@@ -161,11 +161,16 @@ class Caps(Gst.Caps):
     def __getitem__(self, index):
         if index >= self.get_size():
             raise IndexError('structure index out of range')
-        return self.get_structure(index)
+
+        return Gst.Caps.get_structure(self, index)
 
     def __len__(self):
         return self.get_size()
 
+    def get_structure(self, index):
+        return StructureWrapper(_gi_gst.caps_get_structure(self, index), self,
+                                False)
+
     def get_structure_writable(self, index):
         return StructureWrapper(_gi_gst.caps_get_writable_structure(self, index), self, True)
 
@@ -371,6 +376,9 @@ class Structure(Gst.Structure):
         self._writable = False
         pass
 
+    def __ptr__(self):
+        return _gi_gst._get_object_ptr(self)
+
     def __getitem__(self, key):
         return self.get_value(key)
 

subprojects/gst-python/gi/overrides/gstmodule.c

@@ -989,6 +989,29 @@ _gst_caps_make_writable (PyObject * self, PyObject * args)
   return res;
 }
 
+static PyObject *
+_gst_caps_get_structure (PyObject * self, PyObject * args)
+{
+  PyTypeObject *gst_caps_type;
+  PyObject *py_caps, *py_structure;
+  GstCaps *caps;
+  gint idx;
+
+  /* Look up Gst.Caps and Gst.Structure parameters */
+  gst_caps_type = pygobject_lookup_class (_gst_caps_type);
+  if (!PyArg_ParseTuple (args, "O!i", gst_caps_type, &py_caps, &idx))
+    return NULL;
+
+  /* Extract GstCaps from Gst.Caps parameter */
+  caps = GST_CAPS (pygobject_get (py_caps));
+
+  /* Get the structure at the given index */
+  py_structure = pyg_boxed_new (_gst_structure_type,
+      gst_caps_get_structure (caps, idx), FALSE, FALSE);
+
+  return py_structure;
+}
+
 static PyObject *
 _gst_caps_get_writable_structure (PyObject * self, PyObject * args)
 {
@@ -1052,6 +1075,23 @@ _gst_memory_override_unmap (PyObject * self, PyObject * args)
   return success;
 }
 
+
+static PyObject *
+_gst_get_object_ptr (PyObject * self, PyObject * args)
+{
+  PyObject *first_arg;
+
+  first_arg = PyTuple_GetItem (args, 0);
+  gpointer ptr = pygobject_get (first_arg);
+
+  if (ptr == NULL) {
+    PyErr_SetString (PyExc_TypeError, "Expected a PyGObject");
+    return NULL;
+  }
+
+  return PyLong_FromVoidPtr (ptr);
+}
+
 static PyObject *
 _gst_buffer_override_map_range (PyObject * self, PyObject * args)
 {
@@ -1182,9 +1222,11 @@ static PyMethodDef _gi_gst_functions[] = {
   {"buffer_override_unmap", (PyCFunction) _gst_buffer_override_unmap, METH_VARARGS, NULL},
   {"memory_override_map", (PyCFunction) _gst_memory_override_map, METH_VARARGS, NULL},
   {"memory_override_unmap", (PyCFunction) _gst_memory_override_unmap, METH_VARARGS, NULL},
+  {"caps_get_structure", (PyCFunction) _gst_caps_get_structure, METH_VARARGS, NULL},
   {"caps_get_writable_structure", (PyCFunction) _gst_caps_get_writable_structure, METH_VARARGS, NULL},
   {"caps_make_writable", (PyCFunction) _gst_caps_make_writable, METH_VARARGS, NULL},
   {"caps_is_writable", (PyCFunction) _gst_caps_is_writable, METH_VARARGS, NULL},
+  {"_get_object_ptr", (PyCFunction) _gst_get_object_ptr, METH_VARARGS, NULL},
   {NULL, NULL, 0, NULL}
 };
 /* *INDENT-ON* */

subprojects/gst-python/testsuite/test_gst.py

@@ -132,7 +132,8 @@ class TestCaps(TestCase):
             s.set_value("rate", 44100)
         capsfilter.set_property("caps", caps)
         caps = capsfilter.get_property("caps")
-        self.assertEqual(caps[0]["rate"], 44100)
+        with caps.get_structure(0) as s:
+            self.assertEqual(s["rate"], 44100)
 
     def test_writable(self):
         Gst.init(None)
@@ -141,8 +142,38 @@ class TestCaps(TestCase):
         with caps.get_structure_writable(0) as s:
             s.set_value("rate", 44100)
             s.set_value("channels", 2)
-        self.assertEqual(caps[0]["rate"], 44100)
-        self.assertEqual(caps[0]["channels"], 2)
+        with caps.get_structure(0) as s:
+            self.assertEqual(s["rate"], 44100)
+            self.assertEqual(s["channels"], 2)
+
+    def test_delete_caps_while_accessing(self):
+        Gst.init(None)
+        caps = Gst.Caps("audio/x-raw")
+
+        with caps.get_structure_writable(0) as s:
+            del caps
+            s.set_value("rate", 44100)
+            s.set_value("channels", 2)
+            self.assertEqual(s["rate"], 44100)
+            self.assertEqual(s["channels"], 2)
+
+    def test_read_no_copy(self):
+        Gst.init(None)
+        caps = Gst.Caps("audio/x-raw")
+
+        with caps.get_structure(0) as s:
+            ptr = s.__ptr__()
+
+        with caps.get_structure(0) as s:
+            self.assertEqual(ptr, s.__ptr__())
+
+        c2 = caps.mini_object
+        self.assertEqual(c2.refcount, 2)
+        caps.make_writable()
+
+        with caps.get_structure(0) as s:
+            self.assertNotEqual(ptr, s.__ptr__())
+
 
 class TestStructure(TestCase):