带有lxml的子路径的XPath谓词？

Question

我正在尝试理解和发送给我使用ACORD XML表单(保险中的通用格式)的XPath.他们发给我的XPath是(为简洁而截断):

./PersApplicationInfo/InsuredOrPrincipal[InsuredOrPrincipalInfo/InsuredOrPrincipalRoleCd="AN"]/GeneralPartyInfo

我遇到麻烦的地方是Python的lxml库告诉我这[InsuredOrPrincipalInfo/InsuredOrPrincipalRoleCd="AN"]是一个invalid predicate.我无法在XPath规范中的任何地方找到标识此语法的谓词,以便我可以修改此谓词.

是否有关于此谓词选择的文档？此外,这甚至是一个有效的谓词,还是在某个地方被破坏了？

可能相关:

我相信我正在使用的公司是一个MS商店,所以这个XPath可能在C#或该堆栈中的其他语言中有效吗？我不完全确定.

更新:

根据评论需求,这里有一些额外的信息.

XML示例:

<ACORD>
  <InsuranceSvcRq>
    <HomePolicyQuoteInqRq>
      <PersPolicy>
        <PersApplicationInfo>
            <InsuredOrPrincipal>
                <InsuredOrPrincipalInfo>
                    <InsuredOrPrincipalRoleCd>AN</InsuredOrPrincipalRoleCd>
                </InsuredOrPrincipalInfo>
                <GeneralPartyInfo>
                    <Addr>
                        <Addr1></Addr1>
                    </Addr>
                </GeneralPartyInfo>
            </InsuredOrPrincipal>
        </PersApplicationInfo>
      </PersPolicy>
    </HomePolicyQuoteInqRq>
  </InsuranceSvcRq>
</ACORD>

代码示例(使用完整的XPath而不是代码段):

>>> from lxml import etree
>>> tree = etree.fromstring(raw)
>>> tree.find('./InsuranceSvcRq/HomePolicyQuoteInqRq/PersPolicy/PersApplicationInfo/InsuredOrPrincipal[InsuredOrPrincipalInfo/InsuredOrPrincipalRoleCd="AN"]/GeneralPartyInfo/Addr/Addr1')
Traceback (most recent call last):
  File "<console>", line 1, in <module>
  File "lxml.etree.pyx", line 1409, in lxml.etree._Element.find (src/lxml/lxml.etree.c:39972)
  File "/Library/Python/2.5/site-packages/lxml-2.3-py2.5-macosx-10.3-i386.egg/lxml/_elementpath.py", line 271, in find
    it = iterfind(elem, path, namespaces)
  File "/Library/Python/2.5/site-packages/lxml-2.3-py2.5-macosx-10.3-i386.egg/lxml/_elementpath.py", line 261, in iterfind
    selector = _build_path_iterator(path, namespaces)
  File "/Library/Python/2.5/site-packages/lxml-2.3-py2.5-macosx-10.3-i386.egg/lxml/_elementpath.py", line 245, in _build_path_iterator
    selector.append(ops[token[0]](_next, token))
  File "/Library/Python/2.5/site-packages/lxml-2.3-py2.5-macosx-10.3-i386.egg/lxml/_elementpath.py", line 207, in prepare_predicate
    raise SyntaxError("invalid predicate")
SyntaxError: invalid predicate

Answer 1

更改tree.find到tree.xpath.find和findall存在于LXML以提供与ElementTree的的其它实现兼容性.这些方法不实现整个XPath语言.要使用包含更多高级功能的XPath表达式,请使用xpath方法,XPath类或XPathEvaluator.

例如:

import io
import lxml.etree as ET

content='''\
<ACORD>
  <InsuranceSvcRq>
    <HomePolicyQuoteInqRq>
      <PersPolicy>
        <PersApplicationInfo>
            <InsuredOrPrincipal>
                <InsuredOrPrincipalInfo>
                    <InsuredOrPrincipalRoleCd>AN</InsuredOrPrincipalRoleCd>
                </InsuredOrPrincipalInfo>
                <GeneralPartyInfo>
                    <Addr>
                        <Addr1></Addr1>
                    </Addr>
                </GeneralPartyInfo>
            </InsuredOrPrincipal>
        </PersApplicationInfo>
      </PersPolicy>
    </HomePolicyQuoteInqRq>
  </InsuranceSvcRq>
</ACORD>
'''
tree=ET.parse(io.BytesIO(content))
path='//PersApplicationInfo/InsuredOrPrincipal[InsuredOrPrincipalInfo/InsuredOrPrincipalRoleCd="AN"]/GeneralPartyInfo'
result=tree.xpath(path)
print(result)

产量

[<Element GeneralPartyInfo at b75a8194>]

而tree.find收益率

SyntaxError: invalid node predicate