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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 item_selected(self, item=None):

 """Change to the selected document and hide this widget."""

        if item is None:
            item = self.currentItem()

        # stack history is in inverse order
        try:
            index = self.stack_history[-(self.currentRow()+1)]
        except IndexError:
            pass
        else:
            self.editor.set_stack_index(index)
            self.editor.current_changed(index)
        self.hide()