import re
from functools import reduce


ROM_MAPPING = {
    "y": "j",
    "ü": "yu",
    "öi": "eoi",
    "ö": "oe",
    "a": "aa",
    "ä": "a",
    "æ": "ae",
}


def rom_map(jyutping):
    return re.sub(
        "(g|k)u(?!ng|k)",
        "\\1wu",
        reduce(lambda pron, rule: pron.replace(*rule), ROM_MAPPING.items(), jyutping),
    )


converted = rom_map("")

print(converted)