Personal practice for pronouncing numerals in Japanese

numerals.py

import difflib
import math
import random


DIGITS = {
    1: "ichi",
    2: "ni",
    3: "san",
    4: "yon",
    5: "go",
    6: "roku",
    7: "nana",
    8: "hachi",
    9: "kyou",
}
HUNDREDS = {
    1: "hyaku",
    2: "nihyaku",
    3: "sanbyaku",
    4: "yonhyaku",
    5: "gohyaku",
    6: "roppyaku",
    7: "nanahyaku",
    8: "happyaku",
    9: "kyouhyaku",
}


def number_to_romaji(n: int) -> str:
    parts: list[str] = []

    if n == 0:
        return "zero"
    elif n < 0:
        parts.append("mainasu")
        n = abs(n)

    # TODO: 1 trillion -> itchou
    # TODO: 100 million -> ichioku

    ten_thousands, n = divmod(n, 10000)
    if ten_thousands > 0:
        parts.append(number_to_romaji(ten_thousands))
        parts.append("+")
        parts.append("man")

    thousands, n = divmod(n, 1000)
    if thousands == 1:
        parts.append("sen")
    elif thousands > 1:
        parts.append(number_to_romaji(thousands))
        parts.append("+")
        parts.append("sen")

    hundreds, n = divmod(n, 100)
    if hundreds > 0:
        parts.append(HUNDREDS[hundreds])

    tens, n = divmod(n, 10)
    if tens == 1:
        parts.append("juu")
    elif tens > 1:
        parts.append(number_to_romaji(tens))
        parts.append("-")
        parts.append("juu")

    if n in DIGITS:
        parts.append(DIGITS[n])

    s = " ".join(parts)
    s = s.replace(" + ", "")
    s = s.replace(" - ", "-")
    return s


def main() -> None:
    try:
        difficulty = 100

        while True:
            digits = random.randrange(difficulty)
            exp = int(random.uniform(0, math.log10(difficulty) + 1))
            n = digits * 10 ** exp

            expected = number_to_romaji(n)
            answer = input(f"{n}: ").lower().strip()

            underline = underline_diff(expected, answer)
            if underline.isspace():
                print("✅")
                difficulty += 10
            else:
                print("❌", expected)
                if answer:
                    print("  ", underline)

    except Exception:
        print(locals())
        raise


def underline_diff(before: str, after: str) -> str:
    underline = [" "] * len(before)
    s = difflib.SequenceMatcher(None, before, after, autojunk=False)
    for tag, i1, i2, j1, j2 in s.get_opcodes():
        if tag == "equal":
            continue
        elif tag == "insert":
            underline[i1:i1+1] = "^"
        else:
            underline[i1:i2] = ["^"] * (i2 - i1)

    # Skip underlining whitespace
    underline = [" " if c.isspace() else u for c, u in zip(before, underline)]

    return "".join(underline)


if __name__ == "__main__":
    try:
        main()
    except KeyboardInterrupt:
        pass

output.txt

$ python numerals.py
740: nanahyaku yon-juu
✅
4200: yonsan nibyaku
❌ yonsen nihyaku
       ^    ^    
26: ni-juu   
❌ ni-juu roku
          ^^^^