code: def get_subdomain(url):
          
  
          if url not in URLHelper.__cache:
              URLHelper.__cache[url] = urlparse(url)
  
          return ".".join(URLHelper.__cache[url].netloc.split(".")[:-2])
docs: Get the subdomain of the given URL.
  
          Args:
              url (str): The URL to get the subdomain from.
  
          Returns:
              str: The subdomain(s)