integer to english words

 1def numberToWords(self, num):
 2    to19 = 'One Two Three Four Five Six Seven Eight Nine Ten Eleven Twelve ' \
 3           'Thirteen Fourteen Fifteen Sixteen Seventeen Eighteen Nineteen'.split()
 4    tens = 'Twenty Thirty Forty Fifty Sixty Seventy Eighty Ninety'.split()
 5    def words(n):
 6        if n < 20:
 7            return to19[n-1:n]
 8        if n < 100:
 9            return [tens[n/10-2]] + words(n%10)
10        if n < 1000:
11            return [to19[n/100-1]] + ['Hundred'] + words(n%100)
12        for p, w in enumerate(('Thousand', 'Million', 'Billion'), 1):
13            if n < 1000**(p+1):
14                return words(n/1000**p) + [w] + words(n%1000**p)
15    return ' '.join(words(num)) or 'Zero'