同时显示多个axis的legend记得
p1=ax0.bar(x1_list,df['freq'].values,width=width,color='g',align='edge',label='i')

p2=ax1.bar(x2_list,df['percent'].values,width=width,color='b',tick_label=df['word_class'].values,align='edge',label='d')

plt.legend(handles = [p1,p2])