请问jieba.analyse如何只输出关键词对应的idf值

想要的运行结果
一列关键词 一列词频 一列idf
减肥 15 0.***

import jieba
import jieba.analyse
sentence = '' #这里填你要放的字符串

seg_list = jieba.cut(sentence, cut_all=True)
print(", ".join(seg_list))
keywords = jieba.analyse.extract_tags(sentence, topK=20, withWeight=True, allowPOS=('n','nr','ns'))
for i in keywords:
    print(i[0],i[1])