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Solve the following problem using Python, implementing the functions described below, one line at a time
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Description:
 def _get_selected_item(self):
 """The currently selected item"""

        selection = self.get_selection()
        if selection.get_mode() != gtk.SELECTION_SINGLE:
            raise AttributeError('selected_item not valid for select_multiple')
        model, selected = selection.get_selected()
        if selected is not None:
            return self._object_at_sort_iter(selected)