def filter_tweets(df, locName):
    """filters the tweets for those regarding waits at the location.

    Args:
        df: a dataframe with column 'tweet_text'
        locName: the name of the location of interest
    """
    df_wait = df[df['tweet_text'].str.contains('wait')]
    df_filtered = df_wait[df_wait['tweet_text'].str.contains(locName)].copy()
    return df_filtered