How about adding rational fraction to Python?

[mensanator at aol.com]

On Feb 16, 6:50�pm, Carl Banks <pavlovevide... at gmail.com> wrote:
> On Feb 16, 5:51 pm, Jeff Schwab <j... at schwabcenter.com> wrote:
>
> > Carl Banks wrote:
> > > On Feb 16, 3:03 pm, Lie <Lie.1... at gmail.com> wrote:
> > >> Although rationals have its limitations too, it is a much
> > >> better choice compared to floats/Decimals for most cases.
>
> > > Maybe that's true for your use cases, but it's not true for most cases
> > > in general.
>
> > > Rationals are pretty useless for almost any extended calculations,
> > > since the denominator tends to grow in size till it's practically
> > > unusbale,
>
> > What do you mean by "practically unusable?"
>
> So big that a fraction takes 10 minutes to reduce to simplest form and/
> or your hard disk starts thrashing.

Out of curiosity, just how big is that?
I ask because I routinely use extremely big
ints and rationals and haven't seen that.

And I'm talking about numbers with, say,
50000 decimal digits up to numbers with
over a billion bits.

>
> It can easily happen with seemingly innocuous calculations.

Where I've had problems is not the size
of the numbers in the repeated calculations
but the number of calculations, say, millions.

>
> > I heard similar arguments
> > made against big integers at one point ("Primitive types are usually big
> > enough, why risk performance?") but I fell in love with them when I
> > first saw them in Smalltalk, and I'm glad Python supports them natively.
>
> It's not the same argument, though.
>
> Repeated calculations don't make bignums too large to manage unless
> they're growing it exponentially.

My work grows exponentially.

>
> With rationals, the accumulating calculations usually makes the
> denominator grow out of control (unless there's some mitigating
> factor, like in Paul Rubin's example where there were only a ever few
> denominators.)

I don't see any problem there either.

It's entirely possible _I_ won't be able
to use the new Fraction data type. My work
has already left the built-in Python big
ints in the dust in favor of gmpy, so I
have no expectation that the new Fraction
type will be of any use to me.

>
> Carl Banks