แสดงชื่อพรรคที่ไม่มีสมาชิก
Show names of parties that does not have any members.
df1 = pd.DataFrame(columns=['party_name', 'party_id']); df2 = pd.DataFrame(columns=['party_name', 'party_id'])
df1.loc[~df1['party_id'].isin(df2['party_id'])]['party_name']