input: Write a function to determine if a given sentence is an 'affirmative' sentence or a 'negative' sentence. The function should tokenize the sentence, identify negation words, and classify the sentence based on the presence of negation words. If the given sentence is empty, return "Affirmative".
  
  def isAffirmativeorNegative(sentence):
       negationwords = findNegation(sentence)
       if len(negationwords)==0: 
           return "Affirmative" 
       else: 
           return "Negative"
  
  def findNegation(sentence):
       negationwords = {'not', 'never', 'no', 'none', 'non', 'neither',
                        'nobody', 'nowhere', 'cannot', 'couldnt', 'shouldnt', 
                        'wouldnt', 'dont', 'didnt', 'hasnt', 'havent', 'isnt', 'arent'} 
       words = nltk.word_tokenize(sentence)
       neg = []
       for word in words:
           if word in negationwords:
               neg.append(word)
       return neg
  
  assert isAffirmativeorNegative("He always comes late but I dont mind.") == "Negative"
  assert isAffirmativeorNegative("The weather is amazing today.") == "Affirmative"
  assert isAffirmativeorNegative("She has never been to London.") == "Negative"
  assert isAffirmativeorNegative("") == "Affirmative"
output: def isAffirmativeorNegative(sentence):
      negationwords = findNegation(sentence)
      if len(negationwords) == 0:
          return "Affirmative"
      else:
          return "Negative"
  
  def findNegation(sentence):
      negationwords = {'not', 'never', 'no', 'none', 'non', 'neither',
                       'nobody', 'nowhere', 'cannot', 'couldnt', 'shouldnt', 
                       'wouldnt', 'dont', 'didnt', 'hasnt', 'havent', 'isnt', 'arent'} 
      words = nltk.word_tokenize(sentence)
      neg = []
      for word in words:
          if word in negationwords:
              neg.append(word)
      return neg