8000 gh-102555: Fix comment parsing in HTMLParser by serhiy-storchaka · Pull Request #135664 · python/cpython · GitHub
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gh-102555: Fix comment parsing in HTMLParser #135664

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gh-135661: Fix comment parsing in HTMLParser
serhiy-storchaka Jun 18, 2025
0e6d20a
Merge branch 'main' into htmlparser-comment
serhiy-storchaka Jun 25, 2025
f1c9efa
Add more tests: "<!---!>" and "<!--!>".
serhiy-storchaka Jun 25, 2025
< 8000 code class="float-right">0f05afc
Move to gh-102555.
serhiy-storchaka Jun 25, 2025
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18 changes: 17 additions & 1 deletion Lib/html/parser.py
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Original file line number Diff line number Diff line change
Expand Up @@ -29,7 +29,8 @@
starttagopen = re.compile('<[a-zA-Z]')
endtagopen = re.compile('</[a-zA-Z]')
piclose = re.compile('>')
commentclose = re.compile(r'--\s*>')
commentclose = re.compile(r'--!?>')
commentabruptclose = re.compile(r'-?>')
# Note:
# 1) if you change tagfind/attrfind remember to update locatestarttagend too;
# 2) if you change tagfind/attrfind and/or locatestarttagend the parser will
Expand Down Expand Up @@ -309,6 +310,21 @@ def parse_html_declaration(self, i):
else:
return self.parse_bogus_comment(i)

# Internal -- parse comment, return length or -1 if not terminated
# see https://html.spec.whatwg.org/multipage/parsing.html#comment-start-state
def parse_comment(self, i, report=True):
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@Privat33r-dev Privat33r-dev Jun 25, 2025 •
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I wonder if the change should be made in the _markupbase.

cpython/Lib/_markupbase.py

Lines 165 to 175 in c2f2fd4

def parse_comment(self, i, report=1):
rawdata = self.rawdata
if rawdata[i:i+4] != '<!--':
raise AssertionError('unexpected call to parse_comment()')
match = _commentclose.search(rawdata, i+4)
if not match:
return -1
if report:
j = match.start(0)
self.handle_comment(rawdata[i+4: j])
return match.end(0)

If the method is overloaded here, then there are no other use cases, and the original method becomes dead code.
https://github.com/search?q=repo%3Apython%2Fcpython%20parse_comment&type=code

rawdata = self.rawdata
assert rawdata.startswith('<!--', i), 'unexpected call to parse_comment()'
match = commentclose.search(rawdata, i+4)
if not match:
match = commentabruptclose.match(rawdata, i+4)
if not match:
return -1
if report:
j = match.start()
self.handle_comment(rawdata[i+4: j])
return match.end()

# Internal -- parse bogus comment, return length or -1 if not terminated
# see http://www.w3.org/TR/html5/tokenization.html#bogus-comment-state
def parse_bogus_comment(self, i, report=1):
Expand Down
32 changes: 30 additions & 2 deletions Lib/test/test_htmlparser.py
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Expand Up @@ -332,17 +332,45 @@ def test_comments(self):
html = ("<!-- I'm a valid comment -->"
'<!--me too!-->'
'<!------>'
'<!----->'
'<!---->'
# abrupt-closing-of-empty-comment
'<!--->'
'<!-->'
'<!----I have many hyphens---->'
'<!-- I have a > in the middle -->'
'<!-- and I have -- in the middle! -->')
'<!-- and I have -- in the middle! -->'
'<!--incorrectly-closed-comment--!>'
'<!----!>'
'<!----!-->'
'<!---- >-->'
'<!---!>-->'
'<!--!>-->'
# nested-comment
'<!-- <!-- nested --> -->'
'<!--<!-->'
'<!--<!--!>'
)
expected = [('comment', " I'm a valid comment "),
('comment', 'me too!'),
('comment', '--'),
('comment', '-'),
('comment', ''),
('comment', ''),
('comment', ''),
('comment', '--I have many hyphens--'),
('comment', ' I have a > in the middle '),
('comment', ' and I have -- in the middle! ')]
('comment', ' and I have -- in the middle! '),
('comment', 'incorrectly-closed-comment'),
('comment', ''),
('comment', '--!'),
('comment', '-- >'),
('comment', '-!>'),
('comment', '!>'),
('comment', ' <!-- nested '), ('data', ' -->'),
('comment', '<!'),
('comment', '<!'),
]
self._run_check(html, expected)

def test_condcoms(self):
Expand Down
3 changes: 3 additions & 0 deletions Misc/NEWS.d/next/Library/2025-06-18-13-28-08.gh-issue-102555.nADrzJ.rst
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Original file line number Diff line number Diff line change
@@ -0,0 +1,3 @@
Fix comment parsing in :class:`html.parser.HTMLParser`. ``--!>`` now
ends the comment. ``-- >`` no longer ends the comment. Support abnormally
ended empty comments ``<-->`` and ``<--->``.
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