code: def _tokenize(sentence):
      '''Tokenizer and Stemmer'''
  
      _tokens = nltk.word_tokenize(sentence)
      tokens = [stemmer.stem(tk) for tk in _tokens]
      return tokenf _tokenize(sentence):
      '''Tokenizer and Stemmer'''
  
      _tokens = nltk.word_tokenize(sentence)
      tokens = [stemmer.stem(tk) for tk in _tokens]
      return tokens
docs: Tokenizer and Stemmer