when python calls an operator, return a set from the operator flag, this matches the set that python operators themselves return. eg.

{'MODAL'} or... {'FINISHED'}

source/blender/python/intern/bpy_operator.c

@@ -32,6 +32,8 @@
 #include "bpy_rna.h" /* for setting arg props only - pyrna_py_to_prop() */
 #include "bpy_util.h"
 
+#include "RNA_enum_types.h"
+
 #include "WM_api.h"
 #include "WM_types.h"
 
@@ -45,6 +47,7 @@ static PyObject *pyop_call( PyObject * self, PyObject * args)
 	wmOperatorType *ot;
 	int error_val = 0;
 	PointerRNA ptr;
+	int operator_ret= OPERATOR_CANCELLED;
 	
 	char		*opname;
 	PyObject	*kw= NULL; /* optional args */
@@ -94,7 +97,7 @@ static PyObject *pyop_call( PyObject * self, PyObject * args)
 			reports= MEM_mallocN(sizeof(ReportList), "wmOperatorReportList");
 			BKE_reports_init(reports, RPT_STORE);
 
-			WM_operator_call_py(C, ot, context, &ptr, reports);
+			operator_ret= WM_operator_call_py(C, ot, context, &ptr, reports);
 
 			if(BPy_reports_to_error(reports))
 				error_val = -1;
@@ -140,7 +143,9 @@ static PyObject *pyop_call( PyObject * self, PyObject * args)
 		return NULL;
 	}
 
-	Py_RETURN_NONE;
+	/* return operator_ret as a bpy enum */
+	return pyrna_enum_bitfield_to_py(operator_return_items, operator_ret);
+
 }
 
 static PyObject *pyop_as_string( PyObject * self, PyObject * args)

source/blender/python/intern/bpy_rna.c

@@ -424,6 +424,24 @@ static int pyrna_string_to_enum(PyObject *item, PointerRNA *ptr, PropertyRNA *pr
 	return 1;
 }
 
+PyObject *pyrna_enum_bitfield_to_py(EnumPropertyItem *items, int value)
+{
+	PyObject *ret= PySet_New(NULL);
+	const char *identifier[RNA_ENUM_BITFLAG_SIZE + 1];
+
+	if(RNA_enum_bitflag_identifiers(items, value, identifier)) {
+		PyObject *item;
+		int index;
+		for(index=0; identifier[index]; index++) {
+			item= PyUnicode_FromString(identifier[index]);
+			PySet_Add(ret, item);
+			Py_DECREF(item);
+		}
+	}
+
+	return ret;
+}
+
 static PyObject *pyrna_enum_to_py(PointerRNA *ptr, PropertyRNA *prop, int val)
 {
 	PyObject *item, *ret= NULL;

source/blender/python/intern/bpy_rna.h

@@ -79,6 +79,8 @@ int pyrna_py_to_prop(PointerRNA *ptr, PropertyRNA *prop, void *data, PyObject *v
 int pyrna_pydict_to_props(PointerRNA *ptr, PyObject *kw, int all_args, const char *error_prefix);
 PyObject * pyrna_prop_to_py(PointerRNA *ptr, PropertyRNA *prop);
 
+PyObject *pyrna_enum_bitfield_to_py(struct EnumPropertyItem *items, int value);
+
 /* function for registering types */
 PyObject *pyrna_basetype_register(PyObject *self, PyObject *args);
 PyObject *pyrna_basetype_unregister(PyObject *self, PyObject *args);