pixelation: custom XSLT functions with Python and lxml

[Fri, 02 Nov 2012 21:28:57 +0000]
I'll be brief. Because the Python "lxml" module doesn't support XSLT 2.0 functions, I was looking at support for EXSLT [] ... ... but then stumbled on how to write my own functions and call them from stylesheets. Freakin' cool. I like calling it "pxslt" for "Python XSLT" and pronouncing it like "pixelate". :P Example below of the "module" I made; the script that calls it, and the results. Told you I'd be brief. Module: def underscore(context, word): '''Replace whitespace with underscore.''' out = word[0].replace(' ', '_') return out def multiply(context, int_val, int2_val): '''Multiply two integers.''' int_val, int2_val = int(int_val[0]), int(int2_val[0]) return int_val * int2_val def libraryThing(context, isbn): '''Get language for a work based on ISBN using LibraryThing API.''' isbn = isbn[0] import urllib res = urllib.urlopen('' + isbn) res_r = return res_r ##### DO NOT EDIT ##### makes it possible to call the above functions with XSLT def pxslt(): myFunctions = [] gbs = globals() from inspect import isfunction for gb in gbs: if isfunction(gbs[gb]) and gb != 'pxslt': #print gb myFunctions.append(gbs[gb]) from lxml import etree #see: ns = etree.FunctionNamespace('file://libs/') ns.prefix = 'pxsl' for myFunction in myFunctions: name = str(myFunction.func_name) ns[name] = myFunction return ns Usage example: from lxml import etree ##### myXML = etree.XML('''\ <a> <b>Hello. This will appear with whitespaces replaced by underscores.</b> <c>3</c> </a>''') myXSL = etree.XSLT(etree.XML('''\ <xsl:stylesheet version="1.0" xmlns:xsl="" xmlns:pxslt="file://libs/"> <xsl:output method="text" version="1.0" /> <xsl:template match="a"> <xsl:variable name="isbn">9955081260</xsl:variable> <xsl:value-of select="pxslt:libraryThing($isbn)" /> <xsl:text>\n</xsl:text> <!-- Python will line break here --> <xsl:value-of select="pxslt:underscore(b/text())" /> <xsl:text>\n</xsl:text> <!-- Python will line break here --> <xsl:call-template name="mathFunc"> </xsl:call-template> </xsl:template> <xsl:template name="mathFunc"> <xsl:variable name="myNum">10</xsl:variable> <xsl:value-of select="pxslt:multiply(c/text(), $myNum)" /> </xsl:template> </xsl:stylesheet>''')) import pxslt pxslt.pxslt() #get all set up with namespaces and function stuff print(myXSL(myXML)) #myXSL_file = etree.XSLT(etree.parse('foo.xsl')) #for testing with a real XSL file #print(myXSL_file(myXML)) Output: >> lit Hello._This_will_appear_with_whitespaces_replaced_by_underscores. 30 ___________________________________________________________________________ Updated Example for Python 3.6 per Sathish's comment of November, 2019: Module: #!/usr/bin/python3 # import os from lxml import etree NS_URI = "file://" + os.path.basename(__file__) # For info in custom functions in lxml, see: def pxslt(funks): """ @funks is a list of function. """ namespace = None for funk in funks: namespace = etree.FunctionNamespace(NS_URI) namespace.prefix = "pxslt" namespace[funk.__name__] = funk return namespace Usage Example: #!/usr/bin/python3 import pxslt from lxml import etree # create some custom functions to use in XSLT. def underscore(context, word): return word[0].replace(" ", "_") def multiply(context, x, y): return int(x[0]) * int(y[0]) # create some XML to alter via XSLT. myXML = """\ <a> <b>Hello. This will appear with whitespaces replaced by underscores.</b> <c>3</c> </a>""" XML = etree.XML(myXML) # create some XSLT that calls the custom functions. myXSL = """\ <xsl:stylesheet version="1.0" xmlns:pxslt="{NS_URI}" xmlns:xsl=""> <xsl:output method="text" version="1.0"> <xsl:template match="a"> <xsl:value-of select="pxslt:underscore(b/text())"> <xsl:text>\n</xsl:text> <!-- Python will line break here --> <xsl:call-template name="mathFunc"> </xsl:call-template> </xsl:value-of></xsl:template> <xsl:template name="mathFunc"> <xsl:variable name="myNum">10</xsl:variable> <xsl:value-of select="pxslt:multiply(c/text(), $myNum)"> </xsl:value-of></xsl:template> </xsl:output></xsl:stylesheet>""".format(NS_URI=pxslt.NS_URI) XSL = etree.XSLT(etree.XML(myXSL)) # update etree so custom functions are available. pxslt.pxslt([underscore, multiply]) print(XSL(XML))


  1. Sathish [2019-11-18 10:47:29]

    Thanks nitin for prompt response :-)

  2. nitin [2019-11-17 20:29:33]

    Hi Sathish, This was for Python 2. "func_name" is deprecated. I've updated the code and example for Python 3.6 The old module code was gobbling up functions from globals and that's a terrible idea. The new demo code now makes you pass in a list of functions. Regardless, you really shouldn't use this code in production. It's better to refer to the usage in - note the use of decorators.

  3. Sathish [2019-11-17 11:23:04]

    Hi Nitin, this is exactly what am looking for... I am new to Python... will this code work with Python 3.6 as well..? I tried your code exactly as such, it gave me error as as follows, name = str(myFunction.func_name) AttributeError: 'function' object has no attribute 'func_name' then I removed the func_name and tried it, but didn't get any result. Its saying the message as, print(myXSL(myXML)) File "src/lxml/xslt.pxi", line 600, in lxml.etree.XSLT.__call__ lxml.etree.XSLTApplyError: XPath evaluation returned no result. Please advice whats going wrong with copy + paste + execute of your code.

  4. nitin [2017-01-08 16:57:43]

    Hi Rick, I don't use XSLT that much anymore, but if 2.0 is really needed, there's always calling something like Saxon via Java/command line if that's acceptable for your workflow.

  5. Rick Quatro [2017-01-01 03:57:25]

    This is fascinating stuff. I love XSLT and XPath and am relatively new to Python. I have gotten spoiled by XSLT/XPath 2.0 and am disappointed that lxml only supports 1.0. But I like the fact that I can "augment" 1.0 by calling Python functions. I am looking forward to playing with this and seeing if I can make it work in my scripts. I hope XSLT/XPath 2.0 support gets added to lxml or some other Python library. I need to do some fancy grouping and I sure would like to use 2.0's grouping features.