import re


def tweet_to_words(raw_tweet):
    """
    Only keeps ascii characters in the tweet and discards @words

    :param raw_tweet:
    :return:
    """
    letters_only = re.sub("[^a-zA-Z@]", " ", raw_tweet)
    words = letters_only.lower().split()
    meaningful_words = [w for w in words if not re.match("^[@]", w)]
    return " ".join(meaningful_words)