Spreadsheet: proper implementation of mp_subscript of Mapping protocol of PropertySheetPy

src/Mod/Spreadsheet/App/PropertySheetPy.xml

@@ -15,5 +15,17 @@
       <Author Licence="LGPL" Name="Eivind Kvedalen" EMail="eivind@kvedalen.name" />
       <UserDocu>Internal spreadsheet object</UserDocu>
     </Documentation>
+    <Sequence
+        sq_length="false"
+        sq_concat="false"
+        sq_repeat="false"
+        sq_item="false"
+        mp_subscript="true"
+        sq_ass_item="false"
+        mp_ass_subscript="false"
+        sq_contains="false"
+        sq_inplace_concat="false"
+        sq_inplace_repeat="false">
+    </Sequence>
   </PythonExport>
 </GenerateModel>

src/Mod/Spreadsheet/App/PropertySheetPyImp.cpp

@@ -31,23 +31,6 @@
 
 using namespace Spreadsheet;
 
-struct PropertySheetPyInit {
-
-    PyMappingMethods methods;
-
-    PropertySheetPyInit() {
-        methods.mp_length = 0;
-        methods.mp_ass_subscript = 0;
-        methods.mp_subscript = [](PyObject *o, PyObject *key) {
-            return static_cast<PropertySheetPy*>(o)->getPropertySheetPtr()->getPyValue(key);
-        };
-
-        PropertySheetPy::Type.tp_as_mapping = &methods;
-    }
-};
-
-static PropertySheetPyInit _PropertySheetPyInit;
-
 // returns a string which represents the object e.g. when printed in python
 std::string PropertySheetPy::representation(void) const
 {
@@ -66,9 +49,14 @@ int PropertySheetPy::PyInit(PyObject* /*args*/, PyObject* /*kwd*/)
     return 0;
 }
 
+PyObject * PropertySheetPy::mapping_subscript(PyObject * o, PyObject *key)
+{
+    return static_cast<PropertySheetPy*>(o)->getPropertySheetPtr()->getPyValue(key);
+}
+
 PyObject *PropertySheetPy::getCustomAttributes(const char* /*attr*/) const
 {
-    return 0;
+    return nullptr;
 }
 
 int PropertySheetPy::setCustomAttributes(const char* /*attr*/, PyObject* /*obj*/)