ElementTree won't parse comments

[poke]

BPO	8277
Nosy	@amauryfa, @scoder, @florentx

^{Note: these values reflect the state of the issue at the time it was migrated and might not reflect the current state.}

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GitHub fields:

assignee = None
closed_at = <Date 2011-10-29.02:35:58.686>
created_at = <Date 2010-04-01.01:37:44.314>
labels = ['expert-XML', 'type-feature']
title = "ElementTree won't parse comments"
updated_at = <Date 2011-10-29.02:35:58.685>
user = 'https://bugs.python.org/poke'

bugs.python.org fields:

activity = <Date 2011-10-29.02:35:58.685>
actor = 'flox'
assignee = 'none'
closed = True
closed_date = <Date 2011-10-29.02:35:58.686>
closer = 'flox'
components = ['XML']
creation = <Date 2010-04-01.01:37:44.314>
creator = 'poke'
dependencies = []
files = []
hgrepos = []
issue_num = 8277
keywords = []
message_count = 5.0
messages = ['102051', '102078', '102110', '102112', '113322']
nosy_count = 5.0
nosy_names = ['effbot', 'amaury.forgeotdarc', 'scoder', 'poke', 'flox']
pr_nums = []
priority = 'normal'
resolution = 'wont fix'
stage = 'resolved'
status = 'closed'
superseder = None
type = 'enhancement'
url = 'https://bugs.python.org/issue8277'
versions = ['Python 3.2']

[poke]

When using xml.etree.ElementTree to parse external XML files, all XML comments within that file are being stripped out. I guess that happens because there is no comment handler in the expat parser.

Example:

test.xml
--------
<example>
<nodeA />
<!-- some comment -->
<nodeB />
</example>

test.py
-------

from xml.etree import ElementTree
with open( 'test.xml', 'r' ) as f:
    xml = ElementTree.parse( f )
ElementTree.dump( xml )

Result
------
<example>
<nodeA />

<nodeB />
</example>

[amauryfa]

ElementTree does parse comments, it just omit them in the tree.
A quick search lead me to this page: http://effbot.org/zone/element-pi.htm
which can be further simplified:

from xml.etree import ElementTree
class MyTreeBuilder(ElementTree.TreeBuilder):
   def comment(self, data):
       self.start(ElementTree.Comment, {})
       self.data(data)
       self.end(ElementTree.Comment)
with open('c:/temp/t.xml', 'r') as f:
   xml = ElementTree.parse(
       f, parser=ElementTree.XMLParser(target=MyTreeBuilder()))
ElementTree.dump(xml)

Now, should ElementTree do this by default? It's not certain, see how effbot's sample needs to wrap the entire file into another 'document' element.

[poke]

Thanks for your reply, Amaury. That page really might mean that it was not intended for ElementTree to parse such things by default. Although it might be nice if there was some easy way to simply enable it, instead of having to hack it into there and depending on details of some internal code (which might change in the future).

Your code btw. didn't work for me, but based on it and on that effbot page, I came up with the following solution, which works fine.

test.py
-------

from xml.etree import ElementTree

class CommentedTreeBuilder ( ElementTree.XMLTreeBuilder ):
    def __init__ ( self, html = 0, target = None ):
        ElementTree.XMLTreeBuilder.__init__( self, html, target )
        self._parser.CommentHandler = self.handle_comment
    
    def handle_comment ( self, data ):
        self._target.start( ElementTree.Comment, {} )
        self._target.data( data )
        self._target.end( ElementTree.Comment )


with open( 'test.xml', 'r' ) as f:
    xml = ElementTree.parse( f, parser = CommentedTreeBuilder() )
ElementTree.dump( xml )

[amauryfa]

yes, my code uses the newer version of ElementTree which will be included with 2.7 and 3.2

[florentx]

IIUC it works like that by design.
The ElementTree 1.3 (which is part of Python 2.7 and 3.2) allows to define your own parser which parses comments (see previous comments).

Close as "won't fix"?