[Python-ideas] Python Float Update

Nicholas Chammas nicholas.chammas at gmail.com
Mon Jun 1 08:27:57 CEST 2015

I don’t know. Personally, I’d be willing to pay a performance penalty
to avoid reasoning about floating-point arithmetic most of the time,
then “drop into” floats when I need the speed.

This is perhaps a bit off topic for the thread, but +9000 for this.

Having decimal literals or something similar by default, though perhaps
problematic from a backwards compatibility standpoint, is a) user friendly,
b) easily understandable, and c) not surprising to beginners. None of these
qualities apply to float literals.

I always assumed that float literals were mostly an artifact of history or
of some performance limitations. Free of those, why would a language choose
them over decimal literals? When does someone ever expect floating-point
madness, unless they are doing something that is almost certainly not
common, or unless they have been burned in the past?

Every day another programmer gets bitten by floating point stupidities like
this one <http://stackoverflow.com/q/588004/877069>. It would be a big win
to kill this lame “programmer rite of passage” and give people numbers that
work more like how they learned them in school.

The competing proposal is to treat decimal literals as decimal.Decimal

I’m interested in learning more about such a proposal.


On Mon, Jun 1, 2015 at 2:03 AM Jim Witschey <jim.witschey at gmail.com> wrote:

> On Sun, May 31, 2015 at 11:46 PM, Matthias Bussonnier
> <bussonniermatthias at gmail.com> wrote:
> > IIRC (during | after) the language submit at PyCon this year, it was
> said that maybe the stdlib should get
> > less features, not more.
> Rationals (and Decimals) already exist in the standard library. The
> original proposal (as I read it, anyway) is more about the default
> interpretation of, e.g., integer division and decimal-number literals.
> > Side note, Sympy as a IPython ast-hook that will wrap all your integers
> into SymPy Integers and hence
> > give you rationals of whatever you like, if you want to SymPy-plify your
> life.
> Thank you for the pointer -- that's really cool.
> > But for majority of use will it be useful ?
> I believe interpreting "0.1" as 1/10 is more ergonomic than
> representing it as 1.600000023841858 * (2^-4). I see it as being more
> useful -- a better fit -- in most use cases because it's simpler, more
> precise, and more understandable.
> > What would be the performance costs ?
> I don't know. Personally, I'd be willing to pay a performance penalty
> to avoid reasoning about floating-point arithmetic most of the time,
> then "drop into" floats when I need the speed.
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