HTMLParser raises ValueError for numeric character references with many leading zeros

[augusto-rehfeldt]

Bug report

Bug description:

Documented behaviour: HTMLParser documentation, constructor: "If convert_charrefs is True (the default), all character references (except the ones in script/style elements) are automatically converted to the corresponding Unicode characters."

Expected: handle_starttag('div', [('title', 'A')]) without an exception

Actual: ValueError: integer string conversion exceeds the 4300-digit limit; handle_starttag is not called.

import html.parser
import re
import sys

if not hasattr(sys, "set_int_max_str_digits"):
    print("REFUTATION REJECTED: integer-string conversion limit unavailable")
else:
    sys.set_int_max_str_digits(4300)
    text = '<div title="&#' + '0' * 4300 + '65;">'
    match = re.fullmatch(r'<div title="&#([0-9]+);">', text)
    if not match or match[1].lstrip("0") != "65":
        print("REFUTATION REJECTED: input is not a valid decimal reference to U+0041")
    else:
        expected = ("OK", [("div", [("title", chr(65))])])
        events = []

        class Parser(html.parser.HTMLParser):
            def handle_starttag(self, tag, attrs):
                events.append((tag, attrs))

        try:
            Parser(convert_charrefs=True).feed(text)
            actual = ("OK", events)
        except Exception as e:
            actual = ("EXCEPTION", type(e).__name__, str(e))

        if actual != expected:
            print("REFUTATION CONFIRMED:", repr(text),
                  "actual:", actual, "expected:", expected)
        else:
            print("REFUTATION REJECTED: actual matches documented expectation")

Output on Python 3.14.6 (Windows-11-10.0.26220-SP0), standard library html.parser:

0000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000065;">' actual: ('EXCEPTION', 'ValueError', 'Exceeds the limit (4300 digits) for integer string conversion: value has 4302 digits; use sys.set_int_max_str_digits() to increase the limit') expected: ('OK', [('div', [('title', 'A')])])

This report was found and written by an automated property-testing tool I run (bugforge). The reproducer above was executed and its output is pasted unedited; no person reviewed the report before it was filed. The search script is in https://github.com/augusto-rehfeldt/bugforge-results/tree/main/html.parser-20261003-132957-c1

CPython versions tested on:

3.14

Operating systems tested on:

Windows

[ZeroIntensity]

See #158748 (comment).