code: def extract(self, item, list_article_candidate):
          
          list_publish_date = []
  
          for article_candidate in list_article_candidate:
              if article_candidate.publish_date != None:
                  list_publish_date.append((article_candidate.publish_date, article_candidate.extractor))
  
          # If there is no value in the list, return None.
          if len(list_publish_date) == 0:
              return None
  
          # If there are more options than one, return the result from date_extractor.
          list_date_extractor = [x for x in list_publish_date if x[1] == "date_extractor"]
          if len(list_date_extractor) == 0:
  
              # If there is no date extracted by date_extractor, return the first result of list_publish_date.
              return list_publish_date[0][0]
          else:
              return list_date_extractor[0][0]
docs: Compares the extracted publish dates.
  
          :param item: The corresponding NewscrawlerItem
          :param list_article_candidate: A list, the list of ArticleCandidate-Objects which have been extracted
          :return: A string, the most likely publish date