How to debug lxml.etree.XSLTParseError: Invalid expression error

Question

I’m trying to find out why lxml cannot parse an XSL document which consists of a “root” document with various xml:includes. I get an error:

Traceback (most recent call last):
File "s.py", line 10, in <module>
  xslt = ET.XSLT(ET.parse(d))
File "xslt.pxi", line 409, in lxml.etree.XSLT.__init__ (src/lxml/lxml.etree.c:151978)
lxml.etree.XSLTParseError: Invalid expression

That tells me where in the lxml source the error is, but is there a way to get more through lxml about where in the xsl the error is, or should I be using a different method? I’m trying to provide a service that accepts XSL documents, so I don’t have access to an XML editor to debug manually. What I would like to do though is give feedback about why a transformation didn’t succeed.

Asked By: markw

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Source

Answer 1

Looking at the exception’s properties, I see that it has an error_log, but for an xpath error (for example) the log only includes information about where within the xpath the error is, so it’s not especially helpful. For the use-case I describe, having arbitrary users submitting XSLT, there’s not a push-button approach. Instead, it would be probably be easiest to use a combination of schema validation and custom logic to find out where the error is and why it’s an error for the purpose of reporting back to the user.

Answered By: markw

Answer 2

Error in package lxmlxslt.pxi can indicate fault with xslt tempalte, processing errors can be extracted from property transform.error_log. An example:

import lxml
import lxml.etree
xmlPath = '/path/data.xml'
xslPath = '/path/template.xlst'
xslRoot = lxml.etree.parse(xslPath)
transform = lxml.etree.XSLT(xslRoot)
xmlDoc = lxml.etree.parse(xmlPath)
try:
    resultDoc = transform(xmlDoc)
except:
    pass
for entry in transform.error_log:
    print('file', entry.filename 
        , entry.line, entry.column, entry.message
        , entry.domain_name, entry.domain)
        , entry.type_name, entry.type)
        , entry.level_name, entry.level)

Source: errors-and-messages (lxml.de)

Answered By: dank8

How to debug lxml.etree.XSLTParseError: Invalid expression error

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