code: def is_link(url, processed, files):
      
      if url not in processed:
          is_file = url.endswith(BAD_TYPES)
          if is_file:
              files.add(url)
              return False
          return True
      return False
docs: Determine whether or not a link should be crawled
      A url should not be crawled if it
          - Is a file
          - Has already been crawled
  
      Args:
          url: str Url to be processed
          processed: list[str] List of urls that have already been crawled
  
      Returns:
          bool If `url` should be crawled