Since Python standard library doesn't have (to my knowledge, at least) an XSL transformer, and if you happen to have Jython installed, here's how you can do an XSL transformation with Java SDK's libraries:

 from java.io import FileInputStream
 from java.io import ByteArrayOutputStream
 

 from javax.xml.transform import TransformerFactory
 from javax.xml.transform.stream import StreamSource
 from javax.xml.transform.stream import StreamResult
 

 input = FileInputStream("test.xsl")
 xslSource = StreamSource(input)
 xslTemplate = TransformerFactory.newInstance().newTemplates(xslSource);
 transformer = xslTemplate.newTransformer()
 

 output = ByteArrayOutputStream()
 result = StreamResult(output)
 

 source = StreamSource(FileInputStream("source.xml"))
 transformer.transform(source, result)
 

 print output # .. or output.toString()