code: def url(value):
      
      if not url_regex.search(value):
          message = u"{0} is not a valid URL".format(value)
          if url_regex.search('http://' + value):
              message += u". Did you mean: http://{0}".format(value)
          raise ValueError(message)
      return value
docs: Validate a URL.
  
      :param string value: The URL to validate
      :returns: The URL if valid.
      :raises: ValueError