Groups | Search | Server Info | Keyboard shortcuts | Login | Register [http] [https] [nntp] [nntps]

Groups > comp.lang.python > #93018

Re: Calling a function is faster than not calling it?

Show all headers | View raw

Steven D'Aprano <steve+comp.lang.python@pearwood.info> wrote:

> Why is calling a function faster than bypassing the function object and
> evaluating the code object itself? And not by a little, but by a lot?
>
> Here I have a file, eval_test.py:
>
> # === cut ===
> from timeit import Timer
>
> def func():
>     a = 2
>     b = 3
>     c = 4
>     return (a+b)*(a-b)/(a*c + b*c)
>
>
> code = func.__code__
> assert func() == eval(code)
>
> t1 = Timer("eval; func()", setup="from __main__ import func")
> t2 = Timer("eval(code)", setup="from __main__ import code")
>
> # Best of 10 trials.
> print (min(t1.repeat(repeat=10)))
> print (min(t2.repeat(repeat=10)))
>
> # === cut ===
>
>
> Note that both tests include a name lookup for eval, so that as much as
> possible I am comparing the two pieces of code on an equal footing.

They are not on equal footing. The first one only looks up eval, but the second actually calls eval. The overhead of calling eval is what makes the difference. To get them on equal footing you will have to insert an eval call also in the first example.

dummy = compile("0", 'string', "eval")

t1 = Timer("eval(dummy); func()", setup="from __main__ import dummy, func")
t2 = Timer("0; eval(code)", setup="from __main__ import code")

And then you'll see that t1 is slightly slower than t2.
-- 
Piet van Oostrum <piet@vanoostrum.org>
WWW: http://pietvanoostrum.com/
PGP key: [8DAE142BE17999C4]

Back to comp.lang.python | Previous | Next — Previous in thread | Find similar | Unroll thread

Thread

Calling a function is faster than not calling it? Steven D'Aprano <steve+comp.lang.python@pearwood.info> - 2015-05-10 19:58 +1000
  Re: Calling a function is faster than not calling it? Christian Gollwitzer <auriocus@gmx.de> - 2015-05-10 12:34 +0200
    Re: Calling a function is faster than not calling it? Steven D'Aprano <steve+comp.lang.python@pearwood.info> - 2015-05-11 01:04 +1000
  Re: Calling a function is faster than not calling it? Peter Otten <__peter__@web.de> - 2015-05-10 12:43 +0200
    Re: Calling a function is faster than not calling it? Steven D'Aprano <steve+comp.lang.python@pearwood.info> - 2015-05-11 00:49 +1000
      Re: Calling a function is faster than not calling it? Peter Otten <__peter__@web.de> - 2015-05-10 18:14 +0200
      Re: Calling a function is faster than not calling it? Ian Kelly <ian.g.kelly@gmail.com> - 2015-05-10 10:25 -0600
  Re: Calling a function is faster than not calling it? Terry Reedy <tjreedy@udel.edu> - 2015-05-10 12:37 -0400
  Re: Calling a function is faster than not calling it? BartC <bc@freeuk.com> - 2015-05-10 22:08 +0100
    Re: Calling a function is faster than not calling it? Steven D'Aprano <steve+comp.lang.python@pearwood.info> - 2015-05-11 13:58 +1000
      Re: Calling a function is faster than not calling it? BartC <bc@freeuk.com> - 2015-05-11 10:50 +0100
        Re: Calling a function is faster than not calling it? Skip Montanaro <skip.montanaro@gmail.com> - 2015-05-11 09:12 -0500
          Re: Calling a function is faster than not calling it? BartC <bc@freeuk.com> - 2015-05-11 16:01 +0100
            Re: Calling a function is faster than not calling it? Skip Montanaro <skip.montanaro@gmail.com> - 2015-05-11 10:13 -0500
      Re: Calling a function is faster than not calling it? Tony the Tiger <tony@tiger.invalid> - 2015-05-15 01:35 +0000
  Re: Calling a function is faster than not calling it? Stefan Behnel <stefan_ml@behnel.de> - 2015-05-11 08:11 +0200
  Re: Calling a function is faster than not calling it? Piet van Oostrum <piet@vanoostrum.org> - 2015-06-22 23:49 +0200

csiph-web