从XML文件中提取元素，然后使用CelementTree模块写入另一个

Question

我有一个大XML文件，我想提取一些标签并将其写入另一个XML文件。我写了此代码：

import xml.etree.cElementTree as CE
tree = CE.ElementTree()
root = CE.Element("root")
i = 0
for event, elem in CE.iterparse('data.xml'):
    if elem.tag == "ActivityRef":
        print(elem.tag)
        a = CE.Element(elem.tag)
        root.append(elem)
        elem.clear()
        i += 1
    if i == 200:
        break

但我没有得到所需的结果，我得到了：

<root>
  <ActivityRef />
  <ActivityRef />
  <ActivityRef />
  <ActivityRef />
  ...
</root>

而不是这样：

<root>
  <ActivityRef>
    <Id>2008-12-11T20:43:07Z</Id>
  </ActivityRef>
  <ActivityRef>
    <Id>2008-10-11T20:43:07Z</Id>
  </ActivityRef>
  ...
</root>

编辑

输入文件：

<?xml version="1.0" encoding="UTF-8"?>
  <Folders>
    <History>
      <Running>
        <ActivityRef>
          <Id>2009-03-14T17:05:55Z</Id>
        </ActivityRef>
        <ActivityRef>
          <Id>2009-03-13T06:12:42Z</Id>
        </ActivityRef>
        <ActivityRef>
          <Id>2009-03-08T09:00:29Z</Id>
        </ActivityRef>
        <ActivityRef>
          <Id>2009-03-04T19:39:39Z</Id>
        </ActivityRef>
        ...
      </Running>
    </History>
</Folders>

，我还需要从源文件中删除元素。

Answer 1

使用xpath

import xml.etree.ElementTree as ET
data = '''<?xml version="1.0" encoding="UTF-8"?>
  <Folders>
    <History>
      <Running>
        <ActivityRef>
          <Id>2009-03-14T17:05:55Z</Id>
        </ActivityRef>
        <ActivityRef>
          <Id>2009-03-13T06:12:42Z</Id>
        </ActivityRef>
        <ActivityRef>
          <Id>2009-03-08T09:00:29Z</Id>
        </ActivityRef>
        <ActivityRef>
          <Id>2009-03-04T19:39:39Z</Id>
        </ActivityRef>
      </Running>
    </History>
</Folders>'''
root = ET.fromstring(data)
# 'activities' contains the elements you are looking for
activities = root.findall('.//ActivityRef')