Where is the TF-IDF from for the CIDEr?

[bigbrother001]

I want to ask that where do the TD-IDF of a word comes from? I guess maybe it is calculated in another dataset.

[LSKhappychild]

If you go through the class CiderScorer, you can check TD-IDF scores are computed using the oracle you feeded into, using compute_score() in Cider class