code: def get_url_directory_string(url):
          
          domain = UrlExtractor.get_allowed_domain(url)
  
          splitted_url = url.split('/')
  
          # the following commented list comprehension could replace
          # the following for, if not and break statement
          # index = [index for index in range(len(splitted_url))
          #          if not re.search(domain, splitted_url[index]) is None][0]
          for index in range(len(splitted_url)):
              if not re.search(domain, splitted_url[index]) is None:
                  if splitted_url[-1] is "":
                      splitted_url = splitted_url[index + 1:-2]
                  else:
                      splitted_url = splitted_url[index + 1:-1]
                  break
  
          return '_'.join(splitted_url)
docs: Determines the url's directory string.
  
          :param str url: the url to extract the directory string from
          :return str: the directory string on the server