Re: Basic Python Questions - Oct. 31, 2013

From	Robert Kern <robert.kern@gmail.com>
Subject	Re: Basic Python Questions - Oct. 31, 2013
Date	2013-10-31 15:11 +0000
References	(2 earlier) <zOOdnQo2GfCgru_PnZ2dnUVZ_rWdnZ2d@earthlink.com> <877gctd1fn.fsf@dpt-info.u-strasbg.fr> <CAPTjJmownGpi3CDpndp5d2gh91=e-Qadc9GxuK+uXot++K7iKQ@mail.gmail.com> <l4tq6a$v14$1@ger.gmane.org> <CAPTjJmp0KvDRpos2Z6r=g47FF2-afxE1iyyUwCMaThnJM_vawA@mail.gmail.com>
Newsgroups	comp.lang.python
Message-ID	<mailman.1882.1383232306.18130.python-list@python.org> (permalink)

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On 2013-10-31 14:49, Chris Angelico wrote:
> On Fri, Nov 1, 2013 at 1:41 AM, Robert Kern <robert.kern@gmail.com> wrote:
>> On 2013-10-31 14:05, Chris Angelico wrote:
>>>
>>> On Fri, Nov 1, 2013 at 12:17 AM, Alain Ketterlin
>>> <alain@dpt-info.u-strasbg.fr> wrote:
>>>>
>>>> "E.D.G." <edgrsprj@ix.netcom.com> writes:
>>>>
>>>>>         The calculation speed question just involves relatively simple
>>>>> math such as multiplications and divisions and trig calculations such
>>>>> as sin and tan etc.
>>>>
>>>>
>>>> These are not "simple" computations.
>>>>
>>>> Any compiled language (Fortran, C, C++, typically) will probably go much
>>>> faster than any interpreted/bytecode-based language (like python or
>>>> perl, anything that does not use a jit).
>>>
>>>
>>> Well, they may not be simple to do, but chances are you can push the
>>> work down to the CPU/FPU on most modern hardware - that is, if you're
>>> working with IEEE floating point, which I'm pretty sure CPython always
>>> does; not sure about other Pythons. No need to actually calculate trig
>>> functions unless you need arbitrary precision (and even then, I'd bet
>>> the GMP libraries have that all sewn up for you). So the language
>>> doesn't make a lot of difference.
>>
>>
>> Sure it does. Python boxes floats into a PyObject structure. Both Python and
>> C will ultimately implement the arithmetic of "a + b" with an FADD
>> instruction, but Python will do a bunch of pointer dereferencing, hash
>> lookups, and function calls before it gets down to that. All of that
>> overhead typically outweighs the floating point computations down at the
>> bottom, even for the more expensive trig functions.
>
> Of course that's true, but that difference is just as much whether
> you're working with addition or trig functions. That overhead is the
> same. So if, as I said in the other post, you're doing some heavy
> crypto work or something, then yes, all that boxing and unboxing is
> expensive.

Yes, Alain was wrong to suggest that these are not "simple calculations" and 
thus will benefit from a lower-level language. In fact, the relationship is 
reversed. These are *such* simple operations that they do benefit from the 
immediate surrounding code being done in C. The amount of time spent on overhead 
doesn't change based on the operation itself but the immediate surrounding code, 
the inner loops. That's where the language (implementation) matters.

 > Most programs aren't doing that, so the advantage is far
 > less (by proportion).

But we're not talking about most programs. We are talking about the OP's 
programs, which apparently *do* involve lots of iterated floating point 
calculations.

-- 
Robert Kern

"I have come to believe that the whole world is an enigma, a harmless enigma
  that is made terrible by our own mad attempt to interpret it as though it had
  an underlying truth."
   -- Umberto Eco

Thread

Basic Python Questions - Oct. 31, 2013 "E.D.G." <edgrsprj@ix.netcom.com> - 2013-10-31 04:31 -0500
  Re: Basic Python Questions - Oct. 31, 2013 Chris “Kwpolska” Warrick <kwpolska@gmail.com> - 2013-10-31 11:03 +0100
    Re: Basic Python Questions - Oct. 31, 2013 "E.D.G." <edgrsprj@ix.netcom.com> - 2013-10-31 05:38 -0500
      Re: Basic Python Questions - Oct. 31, 2013 Chris “Kwpolska” Warrick <kwpolska@gmail.com> - 2013-10-31 12:30 +0100
      Re: Basic Python Questions - Oct. 31, 2013 Alain Ketterlin <alain@dpt-info.u-strasbg.fr> - 2013-10-31 14:17 +0100
        Re: Basic Python Questions - Oct. 31, 2013 Chris Angelico <rosuav@gmail.com> - 2013-11-01 01:05 +1100
          Re: Basic Python Questions - Oct. 31, 2013 Alain Ketterlin <alain@dpt-info.u-strasbg.fr> - 2013-10-31 15:18 +0100
            Re: Basic Python Questions - Oct. 31, 2013 Chris Angelico <rosuav@gmail.com> - 2013-11-01 01:45 +1100
        Re: Basic Python Questions - Oct. 31, 2013 Mark Lawrence <breamoreboy@yahoo.co.uk> - 2013-10-31 14:15 +0000
          Re: Basic Python Questions - Oct. 31, 2013 Alain Ketterlin <alain@dpt-info.u-strasbg.fr> - 2013-10-31 15:31 +0100
        Re: Basic Python Questions - Oct. 31, 2013 Robert Kern <robert.kern@gmail.com> - 2013-10-31 14:41 +0000
        Re: Basic Python Questions - Oct. 31, 2013 Chris Angelico <rosuav@gmail.com> - 2013-11-01 01:49 +1100
        Re: Basic Python Questions - Oct. 31, 2013 Robert Kern <robert.kern@gmail.com> - 2013-10-31 15:11 +0000
      Re: Basic Python Questions - Oct. 31, 2013 Mark Lawrence <breamoreboy@yahoo.co.uk> - 2013-10-31 13:48 +0000
        Re: Basic Python Questions - Oct. 31, 2013 "E.D.G." <edgrsprj@ix.netcom.com> - 2013-11-03 01:17 -0500
          Re: Basic Python Questions - Oct. 31, 2013 "E.D.G." <edgrsprj@ix.netcom.com> - 2013-11-12 04:21 -0600
            Re: Basic Python Questions - Oct. 31, 2013 Chris Angelico <rosuav@gmail.com> - 2013-11-13 10:05 +1100
      Re: Basic Python Questions - Oct. 31, 2013 rusi <rustompmody@gmail.com> - 2013-10-31 08:48 -0700
        Re: Basic Python Questions - Oct. 31, 2013 "E.D.G." <edgrsprj@ix.netcom.com> - 2013-11-03 00:45 -0500
          Re: Basic Python Questions - Oct. 31, 2013 rusi <rustompmody@gmail.com> - 2013-11-02 23:54 -0700
  Re: Basic Python Questions - Oct. 31, 2013 Roy Smith <roy@panix.com> - 2013-10-31 09:20 -0400
  Re: Basic Python Questions - Oct. 31, 2013 Skip Montanaro <skip@pobox.com> - 2013-10-31 11:14 -0500
  Re: Basic Python Questions - Oct. 31, 2013 William Ray Wing <wrw@mac.com> - 2013-11-01 11:42 -0400
    Re: Basic Python Questions - Oct. 31, 2013 "E.D.G." <edgrsprj@ix.netcom.com> - 2013-11-03 01:28 -0500
  Re: Basic Python Questions - Oct. 31, 2013 Ethan Furman <ethan@stoneleaf.us> - 2013-11-01 11:08 -0700
  Re: Basic Python Questions - Oct. 31, 2013 William Ray Wing <wrw@mac.com> - 2013-11-01 15:17 -0400
  Re: Basic Python Questions - Oct. 31, 2013 "E.D.G." <edgrsprj@ix.netcom.com> - 2013-11-03 01:02 -0500
    Re: Basic Python Questions - Oct. 31, 2013 Steven D'Aprano <steve+comp.lang.python@pearwood.info> - 2013-11-03 07:43 +0000
      Re: Basic Python Questions - Oct. 31, 2013 "E.D.G." <edgrsprj@ix.netcom.com> - 2013-11-03 03:47 -0600
        Re: Basic Python Questions - Oct. 31, 2013 Mark Lawrence <breamoreboy@yahoo.co.uk> - 2013-11-03 10:05 +0000
      Re: Basic Python Questions - Oct. 31, 2013 rusi <rustompmody@gmail.com> - 2013-11-03 10:28 -0800
        Re: Basic Python Questions - Oct. 31, 2013 Mark Lawrence <breamoreboy@yahoo.co.uk> - 2013-11-03 18:58 +0000
          Re: Basic Python Questions - Oct. 31, 2013 rusi <rustompmody@gmail.com> - 2013-11-03 20:07 -0800
    Re: Basic Python Questions - Oct. 31, 2013 Jim Gibson <JimSGibson@gmail.com> - 2013-11-03 10:18 -0800
      Re: Basic Python Questions - Oct. 31, 2013 Grant Edwards <invalid@invalid.invalid> - 2013-11-03 23:16 +0000
      Re: Basic Python Questions - Oct. 31, 2013 "E.D.G." <edgrsprj@ix.netcom.com> - 2013-11-04 23:22 -0600
        Re: Basic Python Questions - Oct. 31, 2013 88888 Dihedral <dihedral88888@gmail.com> - 2013-11-07 06:05 -0800
  Re: Basic Python Questions - Oct. 31, 2013 sigtool@kcl.ac.uk - 2013-11-10 06:40 -0800

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