map/filter/reduce/lambda opinions and background unscientificmini-survey

[Carl Banks]

Steven D'Aprano wrote:
> On Sun, 03 Jul 2005 08:14:28 -0700, Scott David Daniels wrote:
>
> > egbert wrote:
> >> On Sat, Jul 02, 2005 at 08:26:31PM -0700, Devan L wrote:
> >>
> >>>Also, map is easily replaced.
> >>>map(f1, sequence) == [f1(element) for element in sequence]
> >>
> >> How do you replace
> >> map(f1,sequence1, sequence2)
> >> especially if the sequences are of unequal length ?
> >>
> >> I didn't see it mentioned yet as a candidate for limbo,
> >> but the same question goes for:
> >> zip(sequence1,sequence2)
> >
> > OK, you guys are picking on what reduce "cannot" do.
> > The first is [f1(*args) for args in itertools.izip(iter1, iter2)]
>
> And now we get messier and messier... Compare these two idioms:
>
> "Map function f1 to each pair of items from seq1 and seq2."
>
> "Build a list comprehension by calling function f1 with the unpacked list
> that you get from a list built by zipping seq1 and seq2 together in pairs."

The shamelessness with which you inflated the verbosity of the latter
is hilarious.


> Good thing that removing reduce is supposed to make code easier to
> understand, right?

It was a bad example.  I would say most people don't usually just call
a function in the list comp, because, frankly, they don't have to.  A
realistic list comp would look something like this in a real program:

[ x**2 + y**2 for (x,y) in izip(xlist,ylist) ]

Now there's no longer much advantage in conciseness for the map version
(seeing that you'd have to define a function to pass to map), and this
is more readable.


-- 
CARL BANKS