ความเห็นแบบแผนฉบับแก้ไขที่มีการบอกเลิก 21 คืออะไร?
What were the revising conventions commentary with a denunciation of 21?
df = pd.DataFrame(columns=['revising_convention_s_', 'denunciations__september_2011_'])
df.loc[df['denunciations__september_2011_'] == '21', 'revising_convention_s_']