can Python be useful as functional?
Rustom Mody
rustompmody at gmail.com
Tue Sep 18 07:12:00 CEST 2007
The following defines the infinite list of primes as a generator [chap
6.5 of the library]
def sieve(l):
p = l.next()
yield p
for x in sieve(l):
if x % p != 0:
yield x
After that
from itertools import *
>>> [p for i,p in izip(range(10), sieve(count(2)))]
[2, 3, 5, 7, 11, 13, 17, 19, 23, 29]
>>>
I tried to write a shorter generator expression based sieve but cant
get it right.
Can someone help? Heres the non-working code
def si(l):
p = l.next()
yield p
(x for x in si(l) if x % p != 0)
There should be an yield or return somewhere but cant figure it out
On 9/18/07, Lorenzo Stella <lorestar at gmail.com> wrote:
> Hi all,
> I haven't experienced functional programming very much, but now I'm
> trying to learn Haskell and I've learned that: 1) in functional
> programming LISTS are fundmental; 2) any "cycle" in FP become
> recursion.
> I also know that Python got some useful tool such as map, filter,
> reduce... so I told: "let's try some FP-style programming with
> Python!". I took a little example of Haskell:
>
> listprimes :: Integer -> [Integer]
> listprimes n = if n == 0 then sieve [2..] else sieve [2..(n-1)]
> where
> sieve [] = []
> sieve (p:xs) = p : sieve (filter (\x -> mod x p > 0) xs)
>
> and I tried to "translate" it in Python:
>
> def sieve(s):
> if s == []:
> return []
> else:
> return [s[0]] + sieve(filter((lambda x: x % s[0] > 0),
> s[1:]))
>
> def listprimes(n):
> return sieve(range(2,n))
>
> These should be almost the same: listprimes actually lists prime
> integers up to n-1. The result is: Haskell implementation works well,
> maybe it's not the better way to do it, but it does what I wanted.
> Python implementation gives me
>
> RuntimeError: maximum recursion depth exceeded in cmp
>
> My question is: how can we call a language "functional" if it's major
> implementation has a limited stack? Or is my code wrong?
>
> LS
>
> --
> http://mail.python.org/mailman/listinfo/python-list
>
More information about the Python-list
mailing list