code: def _tokenize_corpus(self, corpus):
      pool = Pool(cpu_count())
      tokenized_corpus = pool.map(self.tokenizer, corpus)
      return tokenized_corpus
  
imports: from nboost.plugins import Plugin
  from nboost.delegates import ResponseDelegate
  from nboost.database import DatabaseRow
  import numpy
  from multiprocessing import Pool, cpu_count
  import math
  from nltk.stem import PorterStemmer
  from nltk.tokenize import word_tokenize
  from nltk.corpus import stopwords
  import nltk
label_desc: Use image node_id 3 for calling the BM25 obj's underlying member method code with example usage: obj._tokenize_corpus(corpus) and returns: tokenized_corpus