On May 5, 11:36 pm, alex23 <wuwe...@gmail.com> wrote: > Apart from the presence of 'item' at the beginning of the > list comprehension as opposed to 'b.append(item)' at the > end of the for-loop, how exactly does the listcomp force > you to "bounce [..] back and forth" to follow the logic?
It's precisely the fact that the item is at the beginning which is the main instigator of the bounce. To tranlate [f(x) for x in a] into a loop, you start in the middle, work your way toward the right, then bounce back to the left. I think some of us, perhaps subconsciously, get used to reading that small chunk on the right, then bouncing left. See enough small, flat LCs, and we may be conditioned to think that the general rule is to start with that small chunk on the right and bounce left. When confronted with a long, nested LC then, some of us have the instinct to read the rightmost chunk, then bounce left to the next- rightmost chunk, etc. Essentially, if you see [B A] over and over and over again, when finally confronted with LCs of more "elements", it's not immediately clear that the pattern of increasing nestedness is [B A] => [C A B] => [D A B C] => etc. rather than [B A] => [C B A] => [D C B A] => etc. Maybe we're wired wrong, but there are many of us who find the second pattern more logical, which is why it is so easy for us to mess up the order of the nesting in a more complex LC. John -- http://mail.python.org/mailman/listinfo/python-list
