code: def extract(self, item, list_article_candidate):
          
          list_topimage = []
  
          for article_candidate in list_article_candidate:
              if article_candidate.topimage is not None:
                  # Changes a relative path of an image to the absolute path of the given url.
                  article_candidate.topimage = self.image_absoulte_path(item['url'], article_candidate.topimage)
                  list_topimage.append((article_candidate.topimage, article_candidate.extractor))
  
          # If there is no value in the list, return None.
          if len(list_topimage) == 0:
              return None
  
          # If there are more options than one, return the result from newspaper.
          list_newspaper = [x for x in list_topimage if x[1] == "newspaper"]
          if len(list_newspaper) == 0:
  
              # If there is no topimage extracted by newspaper, return the first result of list_topimage.
              return list_topimage[0][0]
          else:
              return list_newspaper[0][0]
docs: Compares the extracted top images.
  
          :param item: The corresponding NewscrawlerItem
          :param list_article_candidate: A list, the list of ArticleCandidate-Objects which have been extracted
          :return: A string (url), the most likely top image