def get_top_article_ids(n, df):
    "\n    INPUT:\n    n - (int) the number of top articles to return\n    df - (pandas dataframe) df as defined at the top of the notebook \n    \n    OUTPUT:\n    top_articles - (list) A list of the top 'n' article titles \n    \n    "
    article_id_grouped_df = df.groupby(['article_id'])
    top_articles_ids = article_id_grouped_df['user_id'].count().sort_values(ascending=False).iloc[:n].index.tolist()
    return top_articles_ids
INPUT:
n - (int) the number of top articles to return
df - (pandas dataframe) df as defined at the top of the notebook 

OUTPUT:
top_articles - (list) A list of the top 'n' article titles
def get_top_article_ids(n, df):
    "\n    INPUT:\n    n - (int) the number of top articles to return\n    df - (pandas dataframe) df as defined at the top of the notebook \n    \n    OUTPUT:\n    top_articles - (list) A list of the top 'n' article titles \n    \n    "
    article_id_grouped_df = df.groupby(['article_id'])
    top_articles_ids = article_id_grouped_df['user_id'].count().sort_values(ascending=False).iloc[:n].index.tolist()
    return top_articles_ids