code: def attr(self, attr_name, attr_value=None):
  		
  		name = self.__attr_name(attr_name)
  		if attr_value is not None:
  			if WHTTPCookie.cookie_attr_value_check(name, attr_value) is not True:
  				raise ValueError('Unacceptable value passed')
  			if self.__ro_flag:
  				raise RuntimeError('Read-only cookie changing attempt')
  			self.__attrs[name] = attr_value
  			return attr_value
  		return self.__attrs[name]
docs: Return attribute value. Attribute value can be updated with this method. In order to update
  		attribute value attr_value must be set. Cookie attribute value couldn't be changed if cookie is
  		in read-only mode (RuntimeError exception is raised).
  
  		:param attr_name: target attribute name
  		:param attr_value: new value to set
  		:return: str