slices.py

def take(n, seq):
    "Return first n items of the seq as a list"
    return list(islice(seq, n))

def drop(n, seq):
    "Return seq with the first n items removed."
    return list(islice(seq, n, None, 1))

def split_by(n, seq):
    return [take(n, seq), drop(n, seq)]

def slices(seq, start=0, end=None, step=2):
    fun = split_by
    ls = len(seq)
    if ls < step and seq:
        yield (0, ls)
    else:
        if ls % step:
            rng = xrange(ls/step+1)
        else:
            rng = xrange(ls/step)
            
        for i in rng:
            segment = fun(step, seq[start:])
            start += step
            yield segment[0][0], segment[0][-1]