无法在xm中写入更新的值

Question

我可以设置更新的值，但它不会写回xml

 xml_doc = minidom.parse(xml_path)
    item_list = xml_doc.getElementsByTagName('JOB')
    for items in item_list:
        if str(items.attributes['JOBNAME'].value) in parsedXmlData:
            old_value = items.attributes['CMDLINE'].value
            print old_value
            items.setAttribute('CMDLINE', parsedXmlData[str(items.attributes['JOBNAME'].value)])
            print "New Value", items.attributes['CMDLINE'].value

我到底错过了什么