Psycho question

[David C. Ullrich]

In article <dullrich-140224.14525606082008 at text.giganews.com>,
 "David C. Ullrich" <dullrich at sprynet.com> wrote:

> In article 
> <8f0dc2a7-d3bd-4632-a282-9428c910088d at e53g2000hsa.googlegroups.com>,
>  bearophileHUGS at lycos.com wrote:
> 
> > David C. Ullrich:
> > > Thanks. If I can get it installed and it works as advertised
> > > this means I can finally (eventually) finish the process of
> > > dumping MS Windows: the only reason I need it right now is for
> > > the small number of Delphi programs I have for which straight
> > > Python is really not adequate. Been not looking forward to
> > > learning some C or Objective C (or whatever that Mac thing
> > > is) - if I can just "accelerate" a few Python routines that'll
> > > be great.
> > 
> > To have better performance with Psyco you need low-level style code,
> > generally not lazy, etc, and adopt some programming conventions, so
> > you may have to rewrite your routines for max speed.
> 
> Thanks. I would have guessed that I'd want low-level style code;
> that's the sort of thing I have in mind. In fact the only thing
> that seems likely to come up right now is looping through an
> array of bytes, modifying them. The plan is to use the array
> module first to convert a string or a list to an array, outside
> the accelerated part, then maybe do something like
> 
> for j in range(len(bytes)/3):
>   g = (bytes[3*j] + bytes[3*j+1] + bytes[3*j+2])/3
>   bytes[3*j] = bytes[3*j+1] = bytes[3*j+2] = g
> 
> then convert back to a list or string or whatever outside
> the accelerated function.
> 
> Surely something like _that_ is exactly what Psyco is going
> to do well with, yes? 

teehee. Downloaded Psyco. The install actually worked.
Tried exactly what's above with a list of 3 million ints.
Didn't time it carefully, seemed to take about two seconds.
Ran it again, in case the second run would be faster for some reason.
Second was about the same.

Said "import psyco", etc. Ran the routine again, it returned
in _no_ time, perceptually.

This is so cool. Gonna find out whether a decorator that
returns the accelerated function works, just for the fun
of deciding what the name should be: @cool? @wheee?
@wow? @dontblinkyoullmissit?

>(Ok, we're talking about image processing,
> in cases where I can't figure out how to get PIL to do whatever
> directly. So sometimes there will be double loops
> 
> for row in range(width):
>   for col in range(height):
>     do_something[row*width + col]
> 
> but at least for the things I can think of right now it
> shouldn't get much worse than that.)
> 
> The things you mention below sound very interesting - I'm
> going to try Psyco first because unless I'm missing something
> I won't have to learn how to use it. Someday when it turns out
> to be not good enough I'll be in touch...
> 
> > If some of your routines are too much slow there are many ways in
> > Python to write faster modules, like Cython, Weave, Inline, Swig, SIP,
> > ShedSkin, etc. For bioinformatics purposes I have found that Pyd + D
> > language is good for me (I have tried Pyrex too few times, but I have
> > lost my patience trying to track down in a jungle of ugly auto-
> > generated C code where some reference count updates happen. Writing D
> > code is hugely faster/better for me. Even writing a C extension for
> > Python from scratch may be better for me because there aren't hidden
> > things happening everywhere. I presume other people don't share this
> > problems of mine because there are lot of people using Cython now).
> > 
> > Bye,
> > bearophile

-- 
David C. Ullrich