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Re: Fast conversion of numbers to numerator/denominator pairs

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On Fri, Aug 23, 2013 at 9:30 PM, Steven D'Aprano
<steve+comp.lang.python@pearwood.info> wrote:
> Is there a fast way to convert a Decimal into a pair of numbers numerator/
> denominator? It *must* be exact, but it doesn't have to be simplest form.
> For example, Decimal("0.5") => (5, 10) would be okay, although (1, 2)
> would be preferred.
>
>
> I've tried this function:
>
> def convert(d):
>     sign, digits, exp = d.as_tuple()
>     num = int(''.join([str(digit) for digit in digits]))
>     if sign: num = -num
>     return num, 10**-exp
>
>
> which is faster, but not fast enough. Any suggestions?

I time this function at about 33% faster than your version for a
six-digit decimal, and almost 50% faster for a 12-digit decimal.  My
guess would be because it's not calling str() on every individual
digit.

def convert(d):
    exp = d.as_tuple().exponent
    num = int(d.scaleb(-exp))
    return num, 10**-exp

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Fast conversion of numbers to numerator/denominator pairs Steven D'Aprano <steve+comp.lang.python@pearwood.info> - 2013-08-24 03:30 +0000
  Re: Fast conversion of numbers to numerator/denominator pairs Ian Kelly <ian.g.kelly@gmail.com> - 2013-08-24 01:37 -0600
  Re: Fast conversion of numbers to numerator/denominator pairs Ian Kelly <ian.g.kelly@gmail.com> - 2013-08-24 01:50 -0600
  Re: Fast conversion of numbers to numerator/denominator pairs Peter Otten <__peter__@web.de> - 2013-08-24 14:52 +0200
  Re: Fast conversion of numbers to numerator/denominator pairs Tim Delaney <timothy.c.delaney@gmail.com> - 2013-08-25 07:59 +1000
  Re: Fast conversion of numbers to numerator/denominator pairs Tim Delaney <timothy.c.delaney@gmail.com> - 2013-08-25 08:05 +1000

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