Python: Add missing write-back support for Models

Ooops :-)

api/python/models.rs

@@ -131,6 +131,23 @@ impl i_slint_core::model::Model for PyModelShared {
         })
     }
 
+    fn set_row_data(&self, row: usize, data: Self::Data) {
+        Python::with_gil(|py| {
+            let obj = self.self_ref.borrow();
+            let Some(obj) = obj.as_ref() else {
+                eprintln!("Python: Model implementation is lacking self object (in set_row_data)");
+                return;
+            };
+
+            if let Err(err) = obj.call_method1(py, "set_row_data", (row, PyValue::from(data))) {
+                eprintln!(
+                    "Python: Model implementation of set_row_data() threw an exception: {}",
+                    err
+                );
+            };
+        });
+    }
+
     fn model_tracker(&self) -> &dyn i_slint_core::model::ModelTracker {
         &self.notify
     }

api/python/tests/test_models.py

@@ -114,3 +114,35 @@ def test_rust_model_sequence():
     assert len(model) == 5
     assert list(model) == [1, 2, 3, 4, 5]
     assert model[2] == 3
+
+
+def test_model_writeback():
+    compiler = native.ComponentCompiler()
+
+    compdef = compiler.build_from_source("""
+  export component App {
+    width: 300px;
+    height: 300px;
+
+    in-out property<[int]> model;
+    callback write-to-model(int, int);
+    write-to-model(index, value) => {
+        self.model[index] = value
+    }
+
+  }
+    """, "")
+    assert compdef != None
+
+    instance = compdef.create()
+    assert instance != None
+
+    model = models.ListModel([100, 0])
+
+    instance.set_property(
+        "model", model)
+
+    instance.invoke("write-to-model", 1, 42)
+    assert list(instance.get_property("model")) == [100, 42]
+    instance.invoke("write-to-model", 0, 25)
+    assert list(instance.get_property("model")) == [25, 42]