lxml，向子元素添加子元素

Question

我创建了一个看起来像这样的XML。

<?xml version='1.0' encoding='utf-8' standalone='no'?>
<flow xlmns="urn:opendaylight:flow:inventory">
  <strict>false</strict>
  <instructions>
    <instruction>
      <apply-action>
        <action>
          <order>0</order>
          <dec-nw-ttl/>
        </action>
      </apply-action>
    </instruction>
  </instructions>

我把它传给一个函数，这个函数需要两个参数，一个是flow（就是这个XML），另一个是actions（我想添加的新动作列表）：

def add_flow_action(flow, actions):
   for newaction in actions:
      etree.SubElement(action, newaction)
   return flow

这个函数的目的是在名为action的父元素下面添加更多的子元素，让它看起来像这样：

<?xml version='1.0' encoding='utf-8' standalone='no'?>
<flow xlmns="urn:opendaylight:flow:inventory">
  <strict>false</strict>
  <instructions>
    <instruction>
      <apply-action>
        <action>
          <order>0</order>
          <dec-nw-ttl/>
          <new-action-1/>      #Comment: NEW ACTION
          <new-action-2/>      #Comment: NEW ACTION
        </action>
      </apply-action>
    </instruction>
  </instructions>

但是这样做不成功，出现了错误：TypeError: 参数'_parent'类型不正确（期望是lxml.etree._Element，但得到了列表）。

有没有什么办法可以修改这个函数来实现这个功能？

Answer 1

你应该先找到一个 action 元素，然后再在里面创建 SubElement：

from lxml import etree

data = """<?xml version='1.0' encoding='utf-8' standalone='no'?>
<flow xlmns="urn:opendaylight:flow:inventory">
  <strict>false</strict>
  <instructions>
    <instruction>
      <apply-action>
        <action>
          <order>0</order>
          <dec-nw-ttl/>
        </action>
      </apply-action>
    </instruction>
  </instructions>
</flow>
"""


def add_flow_action(flow, actions):
    action = flow.xpath('//action')[0]
    for newaction in actions:
        etree.SubElement(action, newaction)
    return flow

tree = etree.fromstring(data)
result = add_flow_action(tree, ['new-action-1', 'new-action-2'])

print etree.tostring(result)

输出结果是：

<flow xlmns="urn:opendaylight:flow:inventory">
  <strict>false</strict>
  <instructions>
    <instruction>
      <apply-action>
        <action>
          <order>0</order>
          <dec-nw-ttl/>
          <new-action-1/>
          <new-action-2/>
        </action>
      </apply-action>
    </instruction>
  </instructions>
</flow>