Python iterate N items at a time

natatime.py

import itertools

def natatime(n, iterable, fillvalue = None):
  """Returns an iterator yielding `n` elements at a time.

  :param n: the number of elements to return at each iteration
  :param iterable: the iterable over which to iterate
  :param fillvalue: the value to use for missing elements

  :Example:

  >>> for (a,b,c) in natatime(3, [1,2,3,4,5], fillvalue = "?"):
  ...   print a, b, c
  ...
  1 2 3
  4 5 ?
  """
  stepped_slices = ( itertools.islice(iterable, i, None, n) for i in xrange(n) )
  return itertools.izip_longest(*stepped_slices, fillvalue = fillvalue)