Python Lxml(objectify):检查标签是否存在

Question

我需要检查xml文件中是否存在某个标记.

例如,我想查看此代码段中是否存在该标记:

 <main>
       <elem1/>
       <elem2>Hi</elem2>
       <elem3/>
       ...
 </main>

目前,我正在使用一个带有错误检查的丑陋黑客,如下所示:

try:
   if root.elem1.tag:
      foo = elem1
except AttributeError:
   foo = "error finding elem1"

如果无法找到节点,我也想自定义字符串(即"无法找到-tagname-").

我必须检查一长串变量,我不想重复代码100次.

有什么建议？

编辑:

以下是实际xml文件的片段:

<main>
 <asset name="Virtual Dvaered Unpresence">
  <virtual/>
  <presence>
   <faction>Dvaered</faction>
   <value>-1000.000000</value>
   <range>0</range>
  </presence>
 </asset>
 <asset name="Virtual Empire Small">
  <virtual/>
  <presence>
   <faction>Empire</faction>
   <value>100.000000</value>
   <range>2</range>
  </presence>
 </asset>
</main>

我想检查标签是否存在,如果是,则获取内容.

编辑编辑:好的,我将结合两个答案,但我只能投一票.抱歉.

编辑3:关于XPath的相关问题:Python lxml(objectify):Xpath麻烦

Answer 1

hasattr() 适用于此:

if hasattr(root, 'elem1'):
    foo = root.elem1

Answer 2

编辑:样本文件的更新答案.

我假设你想搜索每个资产的某些标签.如果是这样,以下内容对我有用:

import lxml.objectify

# Parse the file.
tree = lxml.objectify.parse('sample.xml')
root = tree.getroot()

# Which elements to find.
to_find = set(['presence/faction', 'presence/value', 'fake'])

# Go through each asset in the document.
for asset in root.findall('asset'):
    # Check for each element. 
    for name in to_find:
        node = asset.find(name)
        if node is not None:
            print 'Found %s, its value is %s' % (name, node)
        else:
            print 'Unable to find %s' % name

输出是:

Found presence/value, its value is -1000.0
Found presence/faction, its value is Dvaered
Unable to find fake
Found presence/value, its value is 100.0
Found presence/faction, its value is Empire
Unable to find fake

Answer 3

假设您想获得elem2的值,您可以使用xpath来查找它.

tree = etree.parse(StringIO(htmlString), etree.HTMLParser()).getroot()
youWantValue = tree.xpath('/main/elem2')[0].text