Re: [lxml] Accessing variables from within an XSL file

10 Apr 2019

      Hi Stefan,

Many thanks for your thoughts.  I hadn't considered just executing an XPath
query directly against the XSL as simple XML – but that works!  I combined
this idea with your xpath expression and now have a function that will
return the correct value:

def get_variable_from_xsl(variable_name, xsl):
    xpath_results = xsl.xpath("//xsl:variable[@name=$name]",
name=variable_name,
                    namespaces={'xsl':'http://www.w3.org/1999/XSL/Transform'
})
    for xpath_result in xpath_results:
        if xpath_result.get('name') == variable_name:
            for xpath_child in xpath_result.getchildren():
                if 'select' in xpath_child.keys():
                    return xpath_child.get('select')
    return None

destination_url = get_variable_from_xsl('destination_url', xsl)
print(f"destination_url = {destination_url}")

Which returns:

destination_url = 'https://my.domain.example.com/'

Thanks again!

aid

On Wed, 10 Apr 2019 at 18:25, Stefan Behnel  wrote:
...
Adrian Bool schrieb am 10.04.19 um 10:49:
...
I'm trying to extract from data from XSL files on an IBM DataPower
system.
I can't change the XSLT files - and therefore need to work around their
current structure to get the info I need.
Well, XSL is XML, so you can always post-process the XSL document after
parsing it as XML, before you pass it into the XSLT() constructor.
...
I'm doing this from within Python 3.7 using etree.__version__ 4.3.3.
Here are my imports, a dummy XML object and a cutdown version of the XSL
file from the IBM system:
from lxml import etree
    from textwrap import dedent
xml = etree.XML("""<root></root>""")
xsl = etree.XML(dedent(
        """<?xml version="1.0"?>
        http://www.w3.org/1999/XSL/Transform"
        xmlns:dp="http://www.datapower.com/extensions"
        extension-element-prefixes="dp">

    xsl:copy

                https://my.domain.example.com/'"
/>

<!--Set the destination URL in the context variable-->

I don't think I've ever tried this myself in lxml. I guess I would have
expected value="{$destination_url}" rather than the plain variable
reference here. Can't say how XSLT is meant to deal with this.
...

        """))
My goal is to use lxml to process this file and extract the contents of
the
...
DataPower variable 'var://context/mpgw/Destination' - i.e. the contents
of
the xsl:variable $destination_url - in the above case '
https://my.domain.example.com/'.
I've created an XSLT extension for the "dp:set-variable" element to try
to
capture this information:
class MyExtElement(etree.XSLTExtension):
        def execute(self, context, self_node, input_node, output_parent):
            if self_node.tag == '{
http://www.datapower.com/extensions}set-variable':
                print(f"Setting variable of name {self_node.get('name')}
to
value {self_node.get('value')}")
extensions = { ('http://www.datapower.com/extensions',
'set-variable')
: MyExtElement() }
    result = etree.XSLT(xsl, extensions=extensions)(xml)
    print(f"Result: {result}")
When this is being called; instead of the value of destination_url I'm
getting the static "$destination_url" string instead - with the output of
the above script being:
Setting variable of name 'var://context/mpgw/Destination' to value
$destination_url
    Result: <?xml version="1.0"?>
    <root/>
I am rather suprised that the $destination_url xsl:variable was not being
evaluated - does anyone know why this is the case?
Given the above, I've been trying to find a way to access the
$destination_url xsl:variable from within my XSLTExtension - but
unfortunately with no luck.
Did you try looking it up in the XSL document via XPath? Something like
.xpath("//xsl:variable[@name=$name]", name="destination_url")
(plus namespaces)
Stefan
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