Subclassing ElementTree parser to retain comments

Question

Trying to use the ElementTree to parse xml files; since by default the parser does not retain comments, used the following code from http://bugs.python.org/issue8277:

import xml.etree.ElementTree as etree

class CommentedTreeBuilder(etree.TreeBuilder):
    """A TreeBuilder subclass that retains comments."""

    def comment(self, data):
        self.start(etree.Comment, {})
        self.data(data)
        self.end(etree.Comment)

parser = etree.XMLParser(target = CommentedTreeBuilder())

The above is in documents.py. Tested with:

class TestDocument(unittest.TestCase):

    def setUp(self):
        filename = os.path.join(sys.path[0], "data", "facilities.xml")
        self.doc = etree.parse(filename, parser = documents.parser)

    def testClass(self):
        print("Class is {0}.".format(self.doc.__class__.__name__))
        #commented out tests.

if __name__ == '__main__':
    unittest.main()

This barfs with:

Traceback (most recent call last):
File "/home/goncalo/documents/games/ja2/modding/mods/xml-overhaul/src/scripts/../tests/test_documents.py", line 24, in setUp
    self.doc = etree.parse(filename, parser = documents.parser)
File "/usr/lib/python3.3/xml/etree/ElementTree.py", line 1242, in parse
    tree.parse(source, parser)
File "/usr/lib/python3.3/xml/etree/ElementTree.py", line 1726, in parse
    parser.feed(data)
IndexError: pop from empty stack

What am I doing wrong? By the way, the xml in the file is valid (as checked by an independent program) and in utf-8 encoding.

note(s):

using Python 3.3. In Kubuntu 13.04, just in case it is relevant. I make sure to use "python3" (and not just "python") to run the test scripts.

edit: here is the sample xml file used; it is very small (let's see if I can get the formatting right):

Subclassing ElementTree parser to retain comments

1 Answers