text: # Natural Language Toolkit: Word Sense Disambiguation Algorithms
  #
  # Authors: Liling Tan <alvations@gmail.com>,
  #          Dmitrijs Milajevs <dimazest@gmail.com>
  #
  # Copyright (C) 2001-2018 NLTK Project
  # URL: <http://nltk.org/>
  # For license information, see LICENSE.TXT
  
  from nltk.corpus import wordnet
  
  
  def lesk(context_sentence, ambiguous_word, pos=None, synsets=None):
      """Return a synset for an ambiguous word in a context.
  
      :param iter context_sentence: The context sentence where the ambiguous word
           occurs, passed as an iterable of words.
      :param str ambiguous_word: The ambiguous word that requires WSD.
      :param str pos: A specified Part-of-Speech (POS).
      :param iter synsets: Possible synsets of the ambiguous word.
      :return: ``lesk_sense`` The Synset() object with the highest signature overlaps.
  
      This function is an implementation of the original Lesk algorithm (1986) [1].
  
      Usage example::
  
          >>> lesk(['I', 'went', 'to', 'the', 'bank', 'to', 'deposit', 'money', '.'], 'bank', 'n')
          Synset('savings_bank.n.02')
  
      [1] Lesk, Michael. "Automatic sense disambiguation using machine
      readable dictionaries: how to tell a pine cone from an ice cream
      cone." Proceedings of the 5th Annual International Conference on
      Systems Documentation. ACM, 1986.
      http://dl.acm.org/citation.cfm?id=318728
      """
  
      context = set(context_sentence)
      if synsets is None:
          synsets = wordnet.synsets(ambiguous_word)
  
      if pos:
          synsets = [ss for ss in synsets if str(ss.pos()) == pos]
  
      if not synsets:
          return None
  
      _, sense = max(
          (len(context.intersection(ss.definition().split())), ss) for ss in synsets
      )
  
      return sense
  