Re: [pygame] converting byte image for display

[Trevor Fancher <trevor@xxxxxxxxxxx>]

On Jan 1, 2006, at 12:59 AM, Guillaume Proux wrote:

> Ouch!
>
> def to_bw(rawbuffer):
>    retstr=''
>    for e in rawbuffer :
>        retstr = retstr + e*3
>    return retstr
>
> This is a typical slow usage of string concat.
> the same loop would be much quicker execute like this
>
> bwbuffer = "".join(map(lambda x:x*3,rawbuffer))
>
> Guillaume

Guillaume,

I am a new python coder and found your one-line replacement for veto's
function pretty neat.  So neat I decided to run some benchmarks to see
if it truly is faster.

From my test it appears veto's original function is faster.  I tested
that with my test_concat function.  I then tested your way with
test_map1 and a way I thought might be a bit faster with test_map2.  As
you can see from the results test_concat seems to have run the fastest.

However, my benchmarking code may be extremely flawed because, as I
said, I am new to python.  If you don't mind, could you correct my
benchmarking code or explain why test_concat is running faster?

Results and code:

trevor@zeppelin ~ $ python bench.py
concat: 5.902
  map1: 9.917
  map2: 9.801

trevor@zeppelin ~ $ cat bench.py
import pygame

def to_bw(rawbuf):
   retstr=''
   for e in rawbuf:
      retstr = retstr + str(e*3)
   return retstr

def test_concat(test_count, test_list):
   t = pygame.time.get_ticks()
   for i in range(test_count):
      a = to_bw(test_list)
   return pygame.time.get_ticks() - t

def test_map1(test_count, test_list):
   t = pygame.time.get_ticks()
   for i in range(test_count):
      a = ''.join(map(lambda x: str(x*3), test_list))
   return pygame.time.get_ticks() - t

def test_map2(test_count, test_list):
   t = pygame.time.get_ticks()
   f = lambda x: str(x*3)
   for i in range(test_count):
      a = ''.join(map(f, test_list))
   return pygame.time.get_ticks() - t

def main():
   test_list = [3, 9, 27]
   test_count = 10**6

   pygame.init()

   print 'concat: '+str(test_concat(test_count, test_list)/1000.0)
   print '  map1: '+str(test_map1(test_count, test_list)/1000.0)
   print '  map2: '+str(test_map2(test_count, test_list)/1000.0)

if __name__ == '__main__':
   main()


Thanks,
__
Trevor Fancher
http://fancher.org/

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