Solving Euler Question 24

I'm learning Clojure by solving project Euler. Here is a python version of one of the solutions.

#!/usr/bin/env python
''' Solving http://projecteuler.net/index.php?section=problems&id=24

Note that Python's 2.6 itertools.permutations return the permutation in order so
we can just write:
    from itertools import islice, permutations
    print islice(permutations(range(10)), 999999, None).next()

And it'll work much faster :)
'''

from itertools import islice, ifilter

def is_last_permutation(n):
    return n == sorted(n, reverse=1)

def next_head(n):
    '''Find next number to be 'head'. 

    It is smallest number if the tail that is bigger than the head.
    In the case of (2 4 3 1) it will pick 3 to get the next permutation
    of (3 1 2 4)
    '''
    return sorted(filter(lambda i: i > n[0], n[1:]))[0]

def remove(element, items):
    return filter(lambda i: i != element, items)

def next_permutation(n):
    if is_last_permutation(n):
        return None

    sub = next_permutation(n[1:])
    if sub:
        return [n[0]] + sub

    head = next_head(n)
    return [head] + sorted([n[0]] + remove(head, n[1:]))

def nth(it, n):
    '''Return the n'th element of an iterator'''
    return islice(it, n, None).next()

def iterate(func, n):
    '''iterate(func, n) -> n, func(n), func(func(n)) ...'''
    while 1:
        yield n
        n = func(n)

def permutations(n):
    return ifilter(None, iterate(next_permutation, n))

if __name__ == "__main__":
    n = range(10)
    m = 1000000
    print "Calculateing the %d permutation of %s" % (m, n)
    print nth(permutations(n), m-1)

pmap

#!/usr/bin/env python
'''Parallel map (Unix only)'''

__author__ = "Miki Tebeka <miki.tebeka@gmail.com>"

# The big advantage of this implementation is that "fork" is very fast on
# copying data, so if you pass big arrays as arguments and return small values
# this is a win

# FIXME 
# * For too many items, we get "Too many open files"
# * Handle child exceptions

from os import fork, pipe, fdopen, waitpid, P_WAIT
from marshal import dump, load
from itertools import takewhile, count

def spawn(func, data):
    read_fo, write_fo = map(fdopen, pipe(), ("rb", "wb"))
    pid = fork()
    if pid: # Parent
        return pid, read_fo

    # Child
    dump(func(data), write_fo)
    write_fo.close()
    raise SystemExit

def wait(child):
    pid, fo = child
    waitpid(pid, P_WAIT)
    value = load(fo)
    fo.close()
    return value

def pmap(func, items):
    '''
    >>> pmap(lambda x: x * 2, range(5))
    [0, 2, 4, 6, 8]
    '''
    children = map(lambda item: spawn(func, item), items)
    return map(wait, children)

if __name__ == "__main__":
    def fib(n):
        a, b = 1, 1
        while n > 1:
            a, b = b, a + b
            n -= 1
        return b

    items = range(10)
    print "pmap(fib, %s)" % str(items)
    print pmap(fib, items)