我想用python替换xml中的空节点

Question

我想用python替换结束语<category/>到Passenger cars </category>。我只需要在类别开始和结束xml标记之间添加“乘用车”

        categories=xml.getElementsByTagName('category')[0].toxml()
        if categories=='<category/>':
            categories=categories.replace('<category/>','<category>Passenger cars</category>')