import numpy
import timeit
import sys

def a(data, y, block_length):
    return data[y * block_length:y * (block_length + 1)] # Slow

def b(data, y, block_length):
    return [data[y * block_length + z] for z in xrange(block_length)] # Fast

if __name__ == "__main__":
    power = 20
    size = 2**power
    data = numpy.zeros(size)

    if 'b' in sys.argv:
        function = b
    else:
        function = a

    for x in xrange(power):
        block_length = 2**x
        blocks = int(size / block_length)

        for y in xrange(blocks):
            block = function(data, y, block_length)