def df2idf(docfreq, totaldocs, log_base=2.0, add=0.0):
    return add + math.log(1.0 * totaldocs / docfreq, log_base)
Compute default inverse-document-frequency for a term with document frequency `doc_freq`::
dataset/ETHPy150Open largelymfs/topical_word_embeddings/TWE-1/gensim/models/tfidfmodel.py/df2idf