Proof of concept of extension class

Class contains XPath extension functions

tests/poc-sdsc.py

@@ -0,0 +1,148 @@
+#!/usr/bin/env python3
+#
+# poc = proof of concept
+#
+# HINT:
+# This file is just a test and can be deleted once all functionality
+# is implemented (also remove poc_confi.ini).
+#
+# HINT 2:
+# If you want to see more or less debug output, open file poc_config.ini,
+# locate section "logger_poc" and change the key "level" to "DEBUG" or
+# "WARN" accordingly.
+#
+# See also:
+# http://lxml.de/extensions.html#xpath-extension-functions
+
+from functools import partial
+import inspect
+import logging
+import logging.config
+import os.path
+import sys
+
+from lxml import etree
+
+
+#
+__version__ = "0.1"
+__author__ = "Thomas Schraitle"
+__license__ = "LGPL-2.1+"
+
+#
+GITHUB_NS = 'https://www.github.com/openSUSE/suse-doc-style-checker'
+GITHUB_PREFIX = 'py'
+#
+HEREDIR = os.path.dirname(os.path.realpath(__file__))
+
+#
+# Set default logging handler to avoid "No handler found" warnings.
+logging.getLogger('poc').addHandler(logging.NullHandler())
+
+logging.config.fileConfig(os.path.join(HEREDIR, 'poc_config.ini'),
+                          disable_existing_loggers=False)
+log = logging.getLogger('poc')
+
+
+class MyXPathExtFunc:
+    """Class which encapsulates XPath extension functions
+    """
+    # Add here your global variables...
+
+    def test(self, context, arg):
+        """Extension function test(arg)"""
+        # Interesting side effect: when called from main_xslt
+        # debug is not displayed. Strange...
+        log.debug("MyXPathExtFunc.test called with: %s", arg)
+        if isinstance(arg, list):
+            arg = arg[0]
+        if isinstance(arg, etree._Element):
+            arg = arg.text
+        return 'test' + arg
+
+
+def getfunctions(cls):
+    """Returns a tuple of all functions of a class 'cls', but ignores
+       functions which starts with '_'
+
+    :param cls: a class
+    :return: a tuple containing function names as strings
+    """
+    # Extract first all names which doesn't start with '_'...
+    names = (func for func in cls.__dict__ if not func.startswith('_'))
+    # then check, if these names are possible functions:
+    return tuple(f for f in names
+                 if inspect.isfunction(cls.__dict__[f]))
+
+
+def setup_namespace():
+    """Setup namespace
+
+    :return: dictionary with prefix:namespace entries
+    """
+    return {GITHUB_PREFIX: GITHUB_NS}
+
+
+def setup_extensions(**args):
+    """Setup XPath extension functions
+    """
+    functions = getfunctions(MyXPathExtFunc)
+    module = MyXPathExtFunc()
+    extensions = etree.Extension(module,
+                                 functions,
+                                 ns=GITHUB_NS
+                                 )
+    return extensions
+
+
+def main_xslt():
+    """Proof of concept of extension function in XSLT"""
+    log.debug('Start.')
+    XSLT = """<xsl:stylesheet version="1.0"
+    xmlns:xsl="http://www.w3.org/1999/XSL/Transform"
+    xmlns:py="{NS}"
+    exclude-result-prefixes="py">
+  <xsl:template match="a">
+    <A><xsl:value-of select="py:test(b)"/></A>
+  </xsl:template>
+</xsl:stylesheet>""".format(NS=GITHUB_NS)
+
+    # Prepare stylesheet tree
+    tree = etree.XML('<a><b>Hiho</b></a>').getroottree()
+    style = etree.XML(XSLT)
+
+    # Create transformation function, pass extension functions
+    transform = etree.XSLT(style,
+                           extensions=setup_extensions())
+    result = transform(tree)
+    log.debug("##### Result #####")
+    print(etree.tostring(result, encoding="unicode"))
+    log.debug('Finished.')
+
+
+def main_xpath():
+    """Proof of concept of extension function in XPath"""
+    log.debug('Start.')
+
+    tree = etree.XML('<a><b>Hiho</b></a>').getroottree()
+    extensions = setup_extensions()
+    ev = etree.XPathEvaluator(tree,
+                              namespaces=setup_namespace(),
+                              extensions=extensions
+                              )
+    log.debug("evaluator: %s", ev)
+    log.debug("extensions: %s", extensions)
+    log.debug("##### Result #####")
+    print(ev("py:test('you')"))
+    log.debug('Finished.')
+
+
+if __name__ == "__main__":
+    log.debug("Started...")
+    try:
+        main_xslt()
+        log.debug("-"*30)
+        main_xpath()
+    except Exception as err:
+        log.error(err, exc_info=True)
+    log.debug("Finished.")

tests/poc_config.ini

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+[loggers]
+keys=root,poc
+
+[handlers]
+keys=consoleHandler
+
+[formatters]
+keys=simpleFormatter
+
+[logger_root]
+level=DEBUG
+handlers=consoleHandler
+
+[logger_poc]
+level=DEBUG
+handlers=consoleHandler
+qualname=poc
+propagate=0
+
+[handler_consoleHandler]
+class=StreamHandler
+level=DEBUG
+formatter=simpleFormatter
+args=(sys.stdout,)
+
+[formatter_simpleFormatter]
+format=[%(levelname)-8s] %(funcName)s: %(message)s
+datefmt=