num2text.py

import math

# Tokens from 1000 and up
_PRONOUNCE = [
	'vigintillion',
	'novemdecillion',
	'octodecillion',
	'septendecillion',
	'sexdecillion',
	'quindecillion',
	'quattuordecillion',
	'tredecillion',
	'duodecillion',
	'undecillion',
	'decillion',
	'nonillion',
	'octillion',
	'septillion',
	'sextillion',
	'quintillion',
	'quadrillion',
	'trillion',
	'billion',
	'million ',
	'thousand ',
	''
]

# Tokens up to 90
_SMALL = {
	'0' : '',
	'1' : 'one',
	'2' : 'two',
	'3' : 'three',
	'4' : 'four',
	'5' : 'five',
	'6' : 'six',
	'7' : 'seven',
	'8' : 'eight',
	'9' : 'nine',
	'10' : 'ten',
	'11' : 'eleven',
	'12' : 'twelve',
	'13' : 'thirteen',
	'14' : 'fourteen',
	'15' : 'fifteen',
	'16' : 'sixteen',
	'17' : 'seventeen',
	'18' : 'eighteen',
	'19' : 'nineteen',
	'20' : 'twenty',
	'30' : 'thirty',
	'40' : 'forty',
	'50' : 'fifty',
	'60' : 'sixty',
	'70' : 'seventy',
	'80' : 'eighty',
	'90' : 'ninety'
}

def get_num(num):
	'''Get token <= 90, return '' if not matched'''
	return _SMALL.get(num, '')

def triplets(l):
	'''Split list to triplets. Pad last one with '' if needed'''
	res = []
	for i in range(int(math.ceil(len(l) / 3.0))):
		sect = l[i * 3 : (i + 1) * 3]
		if len(sect) < 3: # Pad last section
			sect += [''] * (3 - len(sect))
		res.append(sect)
	return res

def norm_num(num):
	"""Normelize number (remove 0's prefix). Return number and string"""
	n = int(num)
	return n, str(n)

def small2eng(num):
	'''English representation of a number <= 999'''
	n, num = norm_num(num)
	hundred = ''
	ten = ''
	if len(num) == 3: # Got hundreds
		hundred = get_num(num[0]) + ' hundred'
		num = num[1:]
		n, num = norm_num(num)
	if (n > 20) and (n != (n / 10 * 10)): # Got ones
		tens = get_num(num[0] + '0')
		ones = get_num(num[1])
		ten = tens + ' ' + ones
	else:
		ten = get_num(num)
	if hundred and ten:
		return hundred + ' ' + ten
		#return hundred + ' and ' + ten
	else: # One of the below is empty
		return hundred + ten

#FIXME: Currently num2eng(1012) -> 'one thousand, twelve'
# do we want to add last 'and'?
def num2text(num):
	'''English representation of a number'''
	num = str(long(num)) # Convert to string, throw if bad number
	if (len(num) / 3 >= len(_PRONOUNCE)): # Sanity check
		raise ValueError('Number too big')

	if num == '0': # Zero is a special case
		return 'zero'

	# Create reversed list
	x = list(num)
	x.reverse()
	pron = [] # Result accumolator
	ct = len(_PRONOUNCE) - 1 # Current index
	for a, b, c in triplets(x): # Work on triplets
		p = small2eng(c + b + a)
		if p:
			pron.append(p + ' ' + _PRONOUNCE[ct])
		ct -= 1
		# Create result
	pron.reverse()
	return ', '.join(pron)