Recursive generation of slice start/end points for a collection for convenient iteration

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, accum=None):
    if accum == None:
        accum = []
    
    if step == 1:
        return seq
    elif step == 0:
        return []
        
    if len(seq) < step and seq:
        accum.append((seq[-(len(seq))], seq[-1]))
        return accum
    elif not seq:
        return accum
    else:
        seg = split_by(step, seq)
        accum.append((seg[0][0], seg[0][-1]))
        return slices(seg[1], start=start, end=end, step=step, accum=accum)