code: def update_headers(self, response):
          
          if 'expires' in response.headers and 'cache-control' in response.headers:
              self.msg = self.server_cache_headers
              return response.headers
          else:
              self.msg = self.default_cache_vars
              date = parsedate(response.headers['date'])
              expires = datetime(*date[:6]) + timedelta(0, self.expire_after)
              response.headers.update({'expires': formatdate(calendar.timegm(expires.timetuple())),
                                  'cache-control': 'public'})
              return response.headers
docs: Returns the updated caching headers.
  
          Args:
              response (HttpResponse): The response from the remote service
  
          Returns:
              response:(HttpResponse.Headers): Http caching headers