On Mar 19, 2:41 pm, "Ben" <[EMAIL PROTECTED]> wrote: > I have recently learned how list comprehension works and am finding it > extremely cool. I am worried, however, that I may be stuffing it into > places that it does not belong. > > What's the most "pythony" way to do this: > > even = [] > for x in range(0,width,2): > for y in range(0,height,2): > color = im.getpixel((x,y)) > even.append(((x,y), color)) > > versus list comprehension: > > even2 = [((x,y), im.getpixel((x,y))) for x in range(0,width,2) for y > in range(0,height,2)] > > Is there a computational difference in creating a blank list and > appending to it versus doing a list comprehension? Are there > advantages to it outside of short and pretty code? > > Feel free to tell me a different way to do this, as well. > > Thanks, > Ben
I have found that I have gone too far when I used listcomps for their sideeffects rather than wanting the list produced, for example the second listcomp below is an expression as statement I don't want the list produced - just the effect on data. >>> # some random ranges >>> data = [range(random.randrange(3,7)) for x in range(4)] >>> # but I want each range jumbled >>> [ random.shuffle(d) for d in data] [None, None, None, None] >>> data [[2, 0, 3, 1], [0, 2, 1], [3, 4, 1, 0, 2], [2, 1, 0, 3]] >>> (I do know how to re-write it). - Paddy. -- http://mail.python.org/mailman/listinfo/python-list
