human
Complete this python program:
def group_albums(session):
assistant
#Here is the Python code you requested.

    """A pipeline stage that groups the items of each task into albums
    using their metadata.
    Groups are identified using their artist and album fields. The
    pipeline stage emits new album tasks for each discovered group.
    """
    def group(item):
        return ((item.albumartist or item.artist), item.album)
    task = None
    while True:
        task = (yield task)
        if task.skip:
            continue
        tasks = []
        sorted_items = sorted(task.items, key=group)
        for (_, items) in itertools.groupby(sorted_items, group):
            items = list(items)
            task = ImportTask(task.toppath, [i.path for i in items], items)
            tasks += task.handle_created(session)
        tasks.append(SentinelImportTask(task.toppath, task.paths))
        task = pipeline.multiple(tasks)