What is the differences between pycocoevalcap Bleu and NLTK Bleu methods for bleu score calculation

Question

For image captioning, Bleu score can by calculated by using pycocoevalcap repo or NLTK Python library like:

`from utils.coco_caption.pycocoevalcap.bleu.bleu import Bleu      # // by pycocoevalcap
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from nltk.translate.bleu_score import corpus_bleu                 # // by nltk

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.`

What is the difference between them?