changing numbers to spellings

[Paul Rubin]

Steve Holden <steve at holdenweb.com> writes:
> You should get some clue about the number conversion (not to menion a
> bunch of code you can lift :) from
> 
>      http://www.python.org/pycon/dc2004/papers/42/ex1-C/num2eng.py

For some reason I felt like writing another one, that doesn't use as
much recursion as the last one I posted.  This one is more like
old-fashioned Python and is shorter, but took several refactorings
and was harder to debug:

def spell(n, d=0):
    # spell arbitrary integer n, restricted to |n| < 10**66
    assert abs(n) < 10**66
    if n == 0: return 'zero'
    if n < 0:  return 'minus ' + spell(-n, d)

    bigtab = ('thousand', 'million', 'billion', 'trillion',
              'quadrillion', 'quintillion', 'sextillion', 'septillion',
              'octillion', 'nonillion', 'decillion', 'undecillion',
              'duodecillion', 'tredecillion', 'quattuordecillion',
              'quinquadecillion', 'sextemdecillion', 'septemdecillion',
              'octodecillion', 'novemdecillion', 'vigintillion')
    smalltab = ('', 'one', 'two', 'three', 'four',
                'five', 'six', 'seven', 'eight', 'nine',
                'ten', 'eleven', 'twelve', 'thirteen', 'fourteen',
                'fifteen', 'sixteen', 'seventeen', 'eighteen', 'nineteen')
    out = []
    def maybe(cond,s): return (cond and s) or ''

    a,n = divmod(n, 1000)
    if a:
        out.extend((spell(a,d+1), maybe(a % 1000, bigtab[d])))

    a,n = divmod(n, 100)
    out.append(maybe(a, '%s hundred'% spell(a)))

    a,b = divmod(n, 10)
    if a > 1:
        out.append(('twenty', 'thirty', 'forty', 'fifty', 'sixty',
                    'seventy', 'eighty', 'ninety')[a-2] +
                   maybe(b, '-' + smalltab[b]))
    else:
        out.append(smalltab[n])
    return (' '.join(filter(bool, out)))

# example
print spell(9**69)