On Fri, Oct 9, 2020 at 3:43 AM Steven D'Aprano <st...@pearwood.info> wrote:
>
> On Thu, Oct 08, 2020 at 11:58:04AM -0400, Random832 wrote:
>
> > I was making a "convert Fraction to Decimal, exactly if possible"
> > function and ran into a wall: it's not possible to do some of the
> > necessary operations with exact precision in decimal:
>
> Of course you can't do them with *exact* precision in Decimal, because
> that only has a fixed precision. (User-configurable, but fixed.)
>
>
> py> from decimal import Decimal
> py> from fractions import Fraction
> py> x = Fraction(1, 3)
> py> Decimal(x.numerator)/x.denominator
> Decimal('0.3333333333333333333333333333')
>
>
You trimmed off the part where the OP said that the denominator would
be only multiples of 2 and/or 5 :)
>>> Fraction(1, 2) ** 53 * Fraction(1, 5) ** 47
Fraction(1, 6400000000000000000000000000000000000000000000000)
>>> Decimal("314159265358979323") / _.denominator
Decimal('4.908738521234051921875E-32')
In theory, this should be precisely representable in decimal, but how
many digits would you need?
ChrisA
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