def take_while(fn, coll):
    """Yield values from coll until fn is False"""
    for e in coll:
        if fn(e):
            yield e
        else:
            return

def partition(n, coll, step=None):
    return take_while(lambda e: len(e) == n,
        (coll[i:i+n] for i in xrange(0, len(coll), step or n)))

def partition_all(n, coll, step=None):
    return (coll[i:i+n] for i in xrange(0, len(coll), step or n))