[wxpython-users] Fast(er) pixel level access

[Christopher Barker]

Folkert Boonstra wrote:
> Just an update on how far i got with getting it faster.
> Replacing loops with list comprehensions is a major enhancement:

I'm a bit surprised -- I thought list comprehensions gave you almost the 
same byte code. I learn something new every day.

Anyway, you can easily get a 10X or so speed up for this kind  of thing 
with numpy -- it really is the tool for the job, it's well worth learning.

on further examination:
     def applyRule(self, rule):
         # Apply the rule
         xdim = ydim = [d for d in range(DIM) if d>0 and d<(DIM-1)]

if xdim = ydim, why make two? though they are references to the same 
thing anyway. (of course, you may be planning to generalize this to when 
x does not equal y)

and: [d for d in range(DIM) if d>0 and d<(DIM-1)] is the same as:

range(1,DIM-1)

Let Python work for you!

Still, if you can make your rule function just take the img array, and 
process it with numpy tools, it will be much faster (less code to get 
wrong, too) -- trust me on this.

-Chris


-- 
Christopher Barker, Ph.D.
Oceanographer

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