See :meth:`~pluginsmanager.observer.observable_list.ObservableList.append()` method

def append(self, item):
        """
        See :meth:`~pluginsmanager.observer.observable_list.ObservableList.append()` method
        """
        self.check_insertion(item)

        self.real_list.append(item)
        self._items |= {item}