On Tue, 05 May 2009 20:36:37 -0700, alex23 wrote:
> On May 6, 4:01 am, "J. Cliff Dyer" <j...@sdf.lonestar.org> wrote:
>> The way you have to bounce your eyes back and forth in the
>> comprehension makes it hard to read the logic. With the loop, on the
>> other hand it is blatantly obvious which way the nesting occurs.
>
>> > >>>> [ item for j in a if len(j)==2 for item in j if item % 2 ]
>> > > ...opposed to...
>> > >>>> for j in a:
>> > > ... if len(j)==2:
>> > > ... for item in j:
>> > > ... if item % 2:
>> > > ... b.append(item) ...
>
>> Much nicer. Thank you.
>
> 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? The only other difference between the two is
> in the layout - the indentation & colons - otherwise they're
> structurally identical.
It's precisely the indentation and colons (plus newlines) that makes
nested for-loops easier to read than list-comps with multiple fors.
for a in alist:
for b in blist:
for c in clist:
if c:
parrot(a, b, c)
is much easier to read than the equivalent one-liner:
[parrot(a, b, c) for a in alist for b in blist for c in clist if c]
You can get back *nearly* all the readability by splitting the list comp
into multiple lines:
[parrot(a, b, c)
for a in alist
for b in blist
for c in clist if c
]
--
Steven
--
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