Ch11 Understanding TF-IDF normalization

[studythink]

The explanation of tfidf shown at page326 as below.

def tfidf(term, document, dataset):
term_freq = document.count(term)
doc_freq = math.log(sum(doc.count(term) for doc in dataset) + 1)
return term_freq / doc_freq

Is it right? According to the formula, the total number of documents in the dataset is not shown in doc_freq.