Parse an XML snippet with regular expressions only.

xml_sax_parse_string.py

import re
from xml.sax.saxutils import unescape


tags_pattern = re.compile(r"</(?P<close>\S+)>|<(?P<open>[^>!?/\s]+)(\s+(?P<attrs>.*?))?(?P<empty>/)?\s*>|<!--(?P<comment>.*?)-->|(?P<cdata><!\[CDATA\[)")
attrs_pattern = re.compile(r"\s*(?P<name>\S+)\s*=\s*(?P<quote>\"|')(?P<value>.*?)(?P=quote)")
cdata_close_pattern = re.compile(r"\]\]>")
escaped_entities = {"&quot;": '"', "&apos;": "'"}


def xml_sax_parse_string(string):
    start = 0

    for match in iter(lambda: tags_pattern.search(string, start), None):
        if start and match.start() != start:
            yield "characters", unescape(string[start:match.start()], escaped_entities)

        if match.group("cdata") is not None:
            start = match.end()
            match = cdata_close_pattern.search(string, start)
            if match is None:
                break

            yield "characters", unescape(string[start:match.start()], escaped_entities)

        elif match.group("open") is not None:
            attrs = {
                name: unescape(value, escaped_entities)
                for name, _, value in attrs_pattern.findall(match.group("attrs") or "")
            }
            yield "startElement", match.group("open"), attrs
            
            if match.group("empty"):
                yield "endElement", match.group("open")

        elif match.group("close") is not None:
            yield "endElement", match.group("close")

        start = match.end()

    if start < len(string) - 1:
        yield "characters", unescape(string[start:], escaped_entities)