Using functional tools

[David Eppstein]

In article <3CD39DAD.D5BC3F9C at vip.fi>, Pekka Niiranen <krissepu at vip.fi> 
wrote:

> I would like to feed every second (or 3rd or 4th .etc) item in a list to
> a function.
> 
> list = ['a', 'b', 'c', 'd', 'e']
> 
> **some fancy map/filter -trick here**
> 
> => list = ['a', function('b'), 'c', function('d'), 'e']
> 
> Is there a (functional) way without using for or while -structures ?

This isn't a functional style, but simple generators allow you to avoid 
all the index manipulation I've seen in previously-posted solutions:

from __future__ import generators

def alternate(L,F):
    L = iter(L)
    while 1:
        yield L.next()
        yield F(L.next())

list = alternate(list,function)

...of course, the result will be an iterator, not a list -- if you 
really want a list, call list(alternate(...)) after being careful not to 
shadow the built-in "list" function...

-- 
David Eppstein       UC Irvine Dept. of Information & Computer Science
eppstein at ics.uci.edu http://www.ics.uci.edu/~eppstein/