English names for numbers

numword.py

__all__ = ['number_words']

WORDS = ["zero", "one", "two", "three", "four", "five", "six", "seven", "eight", "nine", "ten", "eleven", "twelve", "thirteen", "fourteen", "fifteen", "sixteen", "seventeen", "eighteen", "nineteen"]
TENS = [None, None, "twenty", "thirty", "forty", "fifty", "sixty", "seventy", "eighty", "ninety"]
THOUSANDS = {
    False: [None, "thousand", "million", "billion", "trillion", "quadrillion", "quintillion" "sextillion", "septillion", "octillion", "nonillion", "decillion", "hendecillion", "dodecillion", "tridecillion", "tetradecillion", "pentadecillion", "hexadecillion", "heptadecillion", "octadecillion", "enneadecillion", "icosillion"],
    True: [None, "thousand", "million", "milliard", "billion", "billiard", "trillion", "trilliard", "quadrillion", "quadrilliard", "quintillion", "quintilliard" "sextillion", "septillion", "septilliard", "octillion", "octilliard", "nonillion", "nonilliard", "decillion", "decilliard", "hendecillion", "hendecilliard", "dodecillion", "dodecilliard", "tridecillion", "tridecilliard", "tetradecillion", "tetradecilliard", "pentadecillion", "pentadecilliard", "hexadecillion", "hexadecilliard", "heptadecillion", "heptadecilliard", "octadecillion", "octadecilliard", "enneadecillion", "enneadecilliard", "icosillion", "icosilliard"],
}

def number_words(n, long=False, use_and=True, minus="minus"):
    """
    Returns a string of the English name of the given integer.

    long: use the long-scale names, where "billion" = "million million".
      Default is the short-scale names, where "billion" = "thousand million".

    use_and: Include the word "and" in the appropriate places. Typically this
      will be off for US speakers, on for UK speakers.

    minus: The prefix to use for negative numbers. Default is "minus" but you
      can pass "negative" if you want to be pedantic.
    """
    if n < 0:
        return "%s %s" % (minus, number_words(-n, long, use_and))
    if n == 0:
        return WORDS[0]
    groups = []
    while n:
        groups.insert(0, n % 1000)
        n //= 1000
    if len(groups) > len(THOUSANDS[long]):
        raise ValueError("Number too large: %d" % n)
    bits = []
    for i, g in enumerate(groups):
        if g:
            i = len(groups) - i - 1
            if i:
                bits.append("%s %s" % (_subthousand(g, use_and), THOUSANDS[long][i]))
            else:
                bits.append(_subthousand(g, use_and))
    if len(bits) > 1 and groups[-1] > 0 and groups[-1] < 100:
        return "%s %s%s" % (", ".join(bits[:-1]), "and " if use_and else "", bits[-1])
    else:
        return ", ".join(bits)

def _subhundred(n):
    """Returns the name of the number n for 0 < n < 100"""
    if n >= 20:
        if n % 10 != 0:
            return '-'.join([TENS[n//10], WORDS[n%10]])
        else:
            return TENS[n//10]
    else:
        return WORDS[n]

def _subthousand(n, use_and):
    """Returns the name of the number n for 0 < n < 1000"""
    if n >= 100:
        if n % 100 != 0:
            return "%s hundred %s%s" % (WORDS[n//100], "and " if use_and else "", _subhundred(n % 100))
        else:
            return WORDS[n//100] + " hundred"
    else:
        return _subhundred(n % 100)