On Sep 29, 2012 2:38 PM, "Guido van Rossum" <gu...@python.org> wrote: > > On Sat, Sep 29, 2012 at 11:26 AM, Brett Cannon <br...@python.org> wrote: > > > > > > On Sat, Sep 29, 2012 at 9:07 AM, Paul Moore <p.f.mo...@gmail.com> wrote: > >> > >> On 29 September 2012 10:17, Stefan Krah <ste...@bytereef.org> wrote: > >> > Tim Delaney <timothy.c.dela...@gmail.com> wrote: > >> >> If those numbers are similar in other benchmarks, would it be accurate > >> >> and/or > >> >> reasonable to include a statement along the lines of: > >> >> > >> >> "comparable to float performance - usually no more than 3x for > >> >> calculations > >> >> within the range of numbers covered by float" > >> > > >> > For numerical programs, 1.4x (9 digits) to 3x (19 digits) slower would > >> > be > >> > accurate. On Windows the difference is even less. > >> > > >> > For output formatting, cdecimal is faster than float (at least it was > >> > when > >> > I posted a benchmark a couple of months ago). > >> > >> To me, this means that the key point is that for the casual user, > >> float is no longer the "obvious" choice. You'd choose float for the > >> convenience of a built in type, and Decimal for the more natural > >> rounding and precision semantics. If you are sufficiently interested > >> in performance for it to matter, you're no longer a "casual" user. (Up > >> until now, I'd have said use float unless your need for the better > >> behaviour justifies the performance loss - that's no longer the case) > > > > > > Does this mean we want to re-open the discussion about decimal constants? > > Last time this came up I think we decided that we wanted to wait for > > cdecimal (which is obviously here) and work out how to handle contexts, the > > syntax, etc. > > I think that ought to be a Python 4 feature if we ever want it to be a > feature. And I'm not saying this to kill the discussion; I just think > it will be a huge change that we have to consider very carefully. > While the existing float definitely has problems for beginners, it is > incredibly useful for advanced users. Consider e.g. the implications > for numpy / scipy, one of the fastest-growing specialized Python user > communities. > > Now if you want to introduce a new notation for decimals, e.g. 3.14d > and 1e42d, that would be a fine thing. (Should we also have complex > decimals? 1jd anyone?)
That's actually what I meant and not replacing floats (unless a command line flag was used); sorry if that wasn't clear. -brett > > -- > --Guido van Rossum (python.org/~guido)
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