如何让python中的xml根元素只有一个开始标记而没有结束标记？即只有<root>

Question

这是我到目前为止所尝试过的。

from xml.etree.cElementTree import ElementTree
from xml.etree.cElementTree import Element
import os
def write_xml_file(self):
    print os.path.isfile("/home/User_1/Project_Python/Scheduler.xml"),"The file exists ."
    root = Element("backup ")
    tree = ElementTree(root)
    sub_element_1 = Element("first", item_status="1", cur_rec="")
    root.append(sub_element_1)
    sub_element_2 = Element("second", item_recno='2', bksetname=Scheduler.xml_dict['bksetname'], backup_start_time=Scheduler.xml_dict['backup_start_time'],
                            freq=Scheduler.xml_dict['freq'], email=Scheduler.xml_dict['email'])
    root.append(sub_element_2)
    tree.write(open("Scheduler.xml", "w+"))

Sceduler.xml文件输出：

<backup >
    <first cur_rec="" item_status="1" />
    <second backup_start_time="2015-12-08 17:00:09.112524"   bksetname="Default_BackupSet_Admin" email="" freq="[1, 2, 3, 4, 5, 6, 7]" item_recno="2" />
</backup >

我希望只有一个标记作为我的Scheduler.xml文件的根目录，即我该怎么做？