articles = pd.read_csv('articles.csv')
articles = articles[pd.notnull(articles['author'])]
year = articles.groupby(['year'])['id'].nunique().idxmax()
articles['authors'] = articles['author'].apply(lambda L:
    str(L).replace(' and ', ',').replace('&', ',').replace('</strong>', '').replace('<strong>', '').replace('</sub>', '').replace('<sub>', '').split(','))
s = articles.apply(lambda x: pd.Series(x['authors']),axis=1).stack().reset_index(level=1, drop=True)
s.name = 'author'
articles = articles.drop('author', axis=1).join(s)
a = articles.loc[articles['year'] == year]
a.groupby('author')['id'].nunique().nlargest(n=10)