Reading from iterator N elements by a time - the python way.

gistfile1.py

>>> from itertools import *

# First try is like that - OK it works
>>> count = 5
>>> iterator = xrange(100)
>>> list(imap(None, *([iter(iterator)] * count)))
[(0, 1, 2, 3, 4), (5, 6, 7, 8, 9), (10, 11, 12, 13, 14), (15, 16, 17, 18, 19), (20, 21, 22, 23, 24), (25, 26, 27, 28, 29), (30, 31, 32, 33, 34), (35, 36, 37, 38, 39), (40, 41, 42, 43, 44), (45, 46, 47, 48, 49), (50, 51, 52, 53, 54), (55, 56, 57, 58, 59), (60, 61, 62, 63, 64), (65, 66, 67, 68, 69), (70, 71, 72, 73, 74), (75, 76, 77, 78, 79), (80, 81, 82, 83, 84), (85, 86, 87, 88, 89), (90, 91, 92, 93, 94), (95, 96, 97, 98, 99)]

# Apparently imap(None,...) is equivalent to izip() - so we can simplify it
>>> count = 5
>>> iterator = xrange(100)
>>> list(izip(*([iter(iterator)] * count)))
[(0, 1, 2, 3, 4), (5, 6, 7, 8, 9), (10, 11, 12, 13, 14), (15, 16, 17, 18, 19), (20, 21, 22, 23, 24), (25, 26, 27, 28, 29), (30, 31, 32, 33, 34), (35, 36, 37, 38, 39), (40, 41, 42, 43, 44), (45, 46, 47, 48, 49), (50, 51, 52, 53, 54), (55, 56, 57, 58, 59), (60, 61, 62, 63, 64), (65, 66, 67, 68, 69), (70, 71, 72, 73, 74), (75, 76, 77, 78, 79), (80, 81, 82, 83, 84), (85, 86, 87, 88, 89), (90, 91, 92, 93, 94), (95, 96, 97, 98, 99)]

# But it does not works for every length, you see here not all elements are returned
>>> count = 6
>>> iterator = xrange(100)
>>> list(izip(*([iter(iterator)] * count)))
[(0, 1, 2, 3, 4, 5), (6, 7, 8, 9, 10, 11), (12, 13, 14, 15, 16, 17), (18, 19, 20, 21, 22, 23), (24, 25, 26, 27, 28, 29), (30, 31, 32, 33, 34, 35), (36, 37, 38, 39, 40, 41), (42, 43, 44, 45, 46, 47), (48, 49, 50, 51, 52, 53), (54, 55, 56, 57, 58, 59), (60, 61, 62, 63, 64, 65), (66, 67, 68, 69, 70, 71), (72, 73, 74, 75, 76, 77), (78, 79, 80, 81, 82, 83), (84, 85, 86, 87, 88, 89), (90, 91, 92, 93, 94, 95)]

# But you can use izip_longest
>>> count = 6
>>> iterator = xrange(100)
>>> list(izip_longest( *([iter(iterator)] * count)))
[(0, 1, 2, 3, 4, 5), (6, 7, 8, 9, 10, 11), (12, 13, 14, 15, 16, 17), (18, 19, 20, 21, 22, 23), (24, 25, 26, 27, 28, 29), (30, 31, 32, 33, 34, 35), (36, 37, 38, 39, 40, 41), (42, 43, 44, 45, 46, 47), (48, 49, 50, 51, 52, 53), (54, 55, 56, 57, 58, 59), (60, 61, 62, 63, 64, 65), (66, 67, 68, 69, 70, 71), (72, 73, 74, 75, 76, 77), (78, 79, 80, 81, 82, 83), (84, 85, 86, 87, 88, 89), (90, 91, 92, 93, 94, 95), (96, 97, 98, 99, None, None)]

# Third "but", the last element has None, we would like to get rid of them
>>> count = 6
>>> iterator = xrange(100)
>>> list(imap(lambda t: filter(lambda v: v is not None, t), itertools.izip_longest(*([iter(iterator)] * count))))
[(0, 1, 2, 3, 4, 5), (6, 7, 8, 9, 10, 11), (12, 13, 14, 15, 16, 17), (18, 19, 20, 21, 22, 23), (24, 25, 26, 27, 28, 29), (30, 31, 32, 33, 34, 35), (36, 37, 38, 39, 40, 41), (42, 43, 44, 45, 46, 47), (48, 49, 50, 51, 52, 53), (54, 55, 56, 57, 58, 59), (60, 61, 62, 63, 64, 65), (66, 67, 68, 69, 70, 71), (72, 73, 74, 75, 76, 77), (78, 79, 80, 81, 82, 83), (84, 85, 86, 87, 88, 89), (90, 91, 92, 93, 94, 95), (96, 97, 98, 99)]

With some tests:

import unittest
import itertools


def ichunks(seq, n):
    """
    Returns generator of lists being n-element chunks of given sequence.
    """
    seq = iter(seq) # make sure we have generator like sequence
    get_next = lambda: list(itertools.islice(seq, n))
    for items in iter(get_next, []):
        yield items


def gen_range(start, stop):
    while start <= stop:
        yield start
        start += 1


class TestGenRange(unittest.TestCase):

    def test_simple(self):
        self.assertEqual(list(gen_range(1, 3)), [1, 2, 3])
        self.assertEqual(list(gen_range(0, 2)), [0, 1, 2])
        self.assertEqual(list(gen_range(3, 3)), [3])
        self.assertEqual(list(gen_range(3, 4)), [3, 4])


class TestChunks(unittest.TestCase):

    def assertChunksAreFine(self, sequence, n, expected):
        self.assertEqual(list(ichunks(sequence, n)), list(expected))

    def test_simple(self):
        self.assertChunksAreFine(gen_range(1, 6), 3, [[1, 2, 3], [4, 5, 6]])

    def test_with_orphans(self):
        self.assertChunksAreFine(gen_range(1, 5), 2, [[1, 2], [3, 4], [5]])

    def test_list_with_orphans(self):
        self.assertChunksAreFine([1, 2, 3, 4, 5], 3, [
            [1, 2, 3], [4, 5]])

    def test_string_with_orphans(self):
        self.assertChunksAreFine('abcdefghij', 3, [
            ['a', 'b', 'c'], ['d', 'e', 'f'], ['g', 'h', 'i'], ['j']])


if __name__ == '__main__':

    unittest.main()

gen_range is defined for Python 3 (which doesn't have xrange). Besides, xrange is special generator, in example it knows it's length.