Fix leak when directly iterating feature in PyQGIS

Fixes #32944

Author: nyalldawson

python/PyQt6/core/auto_generated/qgsfeature.sip.in

@@ -40,6 +40,9 @@ geometry and a list of field/values attributes.
     QgsAttributes attributes = sipCpp->attributes();
     PyObject *attrs = sipConvertFromType( &attributes, sipType_QgsAttributes, Py_None );
     sipRes = PyObject_GetIter( attrs );
+    // PyObject_GetIter has added a ref to attrs - we need to decrement the ref from sipConvertFromType,
+    // so that the garbage collector will delete attrs when the iterator is deleted
+    Py_DECREF( attrs );
 %End
 
 

python/core/auto_generated/qgsfeature.sip.in

@@ -40,6 +40,9 @@ geometry and a list of field/values attributes.
     QgsAttributes attributes = sipCpp->attributes();
     PyObject *attrs = sipConvertFromType( &attributes, sipType_QgsAttributes, Py_None );
     sipRes = PyObject_GetIter( attrs );
+    // PyObject_GetIter has added a ref to attrs - we need to decrement the ref from sipConvertFromType,
+    // so that the garbage collector will delete attrs when the iterator is deleted
+    Py_DECREF( attrs );
 %End
 
     SIP_PYOBJECT __getitem__( int key ) /HoldGIL/;

src/core/qgsfeature.h

@@ -76,6 +76,9 @@ class CORE_EXPORT QgsFeature
     QgsAttributes attributes = sipCpp->attributes();
     PyObject *attrs = sipConvertFromType( &attributes, sipType_QgsAttributes, Py_None );
     sipRes = PyObject_GetIter( attrs );
+    // PyObject_GetIter has added a ref to attrs - we need to decrement the ref from sipConvertFromType,
+    // so that the garbage collector will delete attrs when the iterator is deleted
+    Py_DECREF( attrs );
     % End
 #endif
 

tests/src/python/test_qgsvectorlayer.py

@@ -320,6 +320,39 @@ def test_FeatureCount(self):
         myCount = myLayer.featureCount()
         self.assertEqual(myCount, 6)
 
+    def test_attribute_iteration(self):
+        layer = QgsVectorLayer(
+            self.get_test_data_path("lines.shp").as_posix(), "Lines", "ogr"
+        )
+        self.assertTrue(layer.isValid())
+        all_attrs = [
+            [attr for attr in feat.attributes()] for feat in layer.getFeatures()
+        ]
+        self.assertCountEqual(
+            all_attrs,
+            [
+                ["Highway", 1.0],
+                ["Highway", 1.0],
+                ["Arterial", 2.0],
+                ["Arterial", 2.0],
+                ["Arterial", 2.0],
+                ["Arterial", 2.0],
+            ],
+        )
+
+        all_attrs = [[attr for attr in feat] for feat in layer.getFeatures()]
+        self.assertCountEqual(
+            all_attrs,
+            [
+                ["Highway", 1.0],
+                ["Highway", 1.0],
+                ["Arterial", 2.0],
+                ["Arterial", 2.0],
+                ["Arterial", 2.0],
+                ["Arterial", 2.0],
+            ],
+        )
+
     # undo stack
     def testUndoStack(self):
         layer = createLayerWithOnePoint()