docs: def next_update(self, value):
          """
          A datetime.datetime object of when the response may next change. This
          should only be set if responses are cached. If responses are generated
          fresh on every request, this should not be set.
          """
  
          if not isinstance(value, datetime):
              raise TypeError(_pretty_message(
                  '''
                  next_update must be an instance of datetime.datetime, not %s
                  ''',
                  _type_name(value)
              ))
  
          self._next_update = value