code: def noun_phrases(text, included_unnormalized=False):
      '''applies normalization to the terms found by noun_phrases_as_tokens
      and joins on '_'.
  
      :rtype: list of phrase strings with spaces replaced by ``_``.
  
      '''
      lemmatizer = nltk.WordNetLemmatizer()
      stemmer = nltk.stem.porter.PorterStemmer()
  
      def normalize(word):
          '''Normalises words to lowercase and stems and lemmatizes it.'''
          word = word.lower()
          try:
              word = stemmer.stem_word(word)
              word = lemmatizer.lemmatize(word)
          except:
              pass
          return word
  
      normalizations = defaultdict(list)
      for terms in noun_phrases_as_tokens(text):
          key = u'_'.join(map(normalize, terms))
          normalizations[key].append(u' '.join(terms))
  
      if included_unnormalized:
          return normalizations.keys(), normalizations
      else:
          return normalizations.keys(f noun_phrases(text, included_unnormalized=False):
      '''applies normalization to the terms found by noun_phrases_as_tokens
      and joins on '_'.
  
      :rtype: list of phrase strings with spaces replaced by ``_``.
  
      '''
      lemmatizer = nltk.WordNetLemmatizer()
      stemmer = nltk.stem.porter.PorterStemmer()
  
      def normalize(word):
          '''Normalises words to lowercase and stems and lemmatizes it.'''
          word = word.lower()
          try:
              word = stemmer.stem_word(word)
              word = lemmatizer.lemmatize(word)
          except:
              pass
          return word
  
      normalizations = defaultdict(list)
      for terms in noun_phrases_as_tokens(text):
          key = u'_'.join(map(normalize, terms))
          normalizations[key].append(u' '.join(terms))
  
      if included_unnormalized:
          return normalizations.keys(), normalizations
      else:
          return normalizations.keys()
docs: applies normalization to the terms found by noun_phrases_as_tokens
      and joins on '_'.
  
      :rtype: list of phrase strings with spaces replaced by ``_``.