03_cancelling_coroutines.py 文件源码

def get_comments_of_top_stories(loop, session, limit, iteration):
    """Retrieve top stories in HN.

    """
    fetcher = URLFetcher()  # create a new fetcher for this task
    try:
        response = await fetcher.fetch(session, TOP_STORIES_URL)
    except BoomException as e:
        log.error("Error retrieving top stories: {}".format(e))
        # return instead of re-raising as it will go unnoticed
        return
    except Exception as e:  # catch generic exceptions
        log.error("Unexpected exception: {}".format(e))
        return

    tasks = {
        asyncio.ensure_future(
            post_number_of_comments(loop, session, fetcher, post_id)
        ): post_id for post_id in response[:limit]}

    # return on first exception to cancel any pending tasks
    done, pending = await asyncio.wait(
        tasks.keys(), return_when=FIRST_EXCEPTION)

    # if there are pending tasks is because there was an exception
    # cancel any pending tasks
    for pending_task in pending:
        pending_task.cancel()

    # process the done tasks
    for done_task in done:
        # if an exception is raised one of the Tasks will raise
        try:
            print("Post {} has {} comments ({})".format(
                tasks[done_task], done_task.result(), iteration))
        except BoomException as e:
            print("Error retrieving comments for top stories: {}".format(e))

    return fetcher.fetch_counter