nested for loop

[Dan Bishop]

wjb131 at web.de (Wolfgang Buechel) wrote in message news:<4629559b.0405101330.286ddb32 at posting.google.com>...
> Hi,
> 
> I want to iterate over all 2x2 matrices with elements in range 0..25 
> (crypto-stuff). 
> 
> To produce them, first I wrote a fourfold nested for loop:
...
> Then I had a look in comp.lang.python and found:
> 
> 
> for (a,b,c,d) in [(x,y,z,t)  for x in range(M)
>                              for y in range(M)
>                              for z in range(M)
>                              for t in range(M)] :
>    matr = [[a,b],[c,d]]

This may be shorter, but it's slower.  Your old code took "only" 1.5
seconds to run on this computer, but the new way takes 3.5 seconds.

What you *can* do to make your code faster (if you don't change matr
once it's created) is to precompute the 676 possible matrix rows.

   ELEMENT_RANGE = range(26)
   MATRIX_ROWS = [[x, y] for x in ELEMENT_RANGE
                         for y in ELEMENT_RANGE]
   for row1 in MATRIX_ROWS:
      for row2 in MATRIX_ROWS:
         matr = [row1, row2]

That takes only 532 ms -- almost 3 times faster than the original.