def retweet_proportion(tweets):
    
    """
    Returns percentage of retweets in a list of tweets.
    Raises error if list is empty.

    :param tweets: the list of tweets, represented as dictionaries.
    :return: float. the percentage of retweets in 'tweets', a number between 0 and 100.
    """

    retweets = 0
    original = 0

    for tweet in tweets:
        if(tweet["rt_status"]):
            retweets += 1
        else:
            original += 1

    try:
        proportion = retweets/(retweets+original)
        return proportion*100

    except ZeroDivisionError:
        print("No tweets found.")