python - "lxml.etree.XPathEvalError: Invalid expression"带有 Unicode 元素名称

Question

lxml 很好地支持 Unicode 元素名称，因为它们根据 XML 规范是有效的。但是在 XPath 中使用 Unicode 会产生错误:

>>> import lxml.etree
>>> e = lxml.etree.fromstring('<?xml version="1.0" encoding="UTF-8"?><элемент>текст</элемент>'.encode('utf-8'))
>>> e.xpath('/элемент/text()')
Traceback (most recent call last):
  File "<stdin>", line 1, in <module>
  File "lxml.etree.pyx", line 1509, in lxml.etree._Element.xpath (src/lxml/lxml.etree.c:50702)
  File "xpath.pxi", line 318, in lxml.etree.XPathElementEvaluator.__call__ (src/lxml/lxml.etree.c:145954)
  File "xpath.pxi", line 238, in lxml.etree._XPathEvaluatorBase._handle_result (src/lxml/lxml.etree.c:144962)
  File "xpath.pxi", line 224, in lxml.etree._XPathEvaluatorBase._raise_eval_error (src/lxml/lxml.etree.c:144817)
lxml.etree.XPathEvalError: Invalid expression

这是 lxml 限制吗？我在文档中找不到它，但也许我错过了。

有人可以解释一下这背后的原因吗？

<小时/> 更新: 仅当 XPath 的第二个字符是西里尔字母时，问题才会重现。它适用于:

• 相对路径，例如//элемент

• 第一个英文字母的路径，例如 //qлемент

• /./элемент 而不是 /элемент (它们是等效的)

而且，这似乎是 libxml2 问题，而不仅仅是 lxml 问题。

$ xmlstarlet sel -t -v "/элемент/text()" test.xml 
Invalid expression: /элемент/text()
compilation error: element with-param
XSLT-with-param: Failed to compile select expression '/элемент/text()'
$ xmlstarlet sel -t -v "/./элемент/text()" test.xml 
текст

我放弃了这个问题，转而使用 /./ 来获取带有西里尔字母标记的绝对 XPath。

Answer 1

如果引用根节点，您的 XPath 缺少 /:

>>> e.xpath('//элемент/text()')
['текст']

或者两个点..(如果引用相对父节点):

>>> e.xpath('../элемент/text()')
['текст']