Shuffled iterator with lookahead

shuffled_iterator.py

def shuffled_iterator(iterator, look_ahead=5000, skip=0, seed=None):
    """Return an iterator on the shuffled (part) of the provided *iterator*.
    This iterator consumes the provided iterator to turn it into a shuffled
    version. The cunsumption can be limited by the *lookahead* argument that
    limits the view of the operator. The *skip* argument flushes the first n
    items of the provided *iterator* and the *seed* allow for repetability.
    """
    rng = numpy.random.RandomState(seed)
    
    batch = list(itertools.islice(iterator, skip, skip+look_ahead))
    rng.shuffle(batch)
    
    next_item = next(iterator, None)
    while next_item:
        yield batch.pop(0)
        idx = rng.randint(0, look_ahead)
        batch.insert(idx, next_item)
        next_item = next(iterator, None)