def process_batch(self, key, tups):
raise NotImplementedError()<EOL>
Process a batch of Tuples. Should be overridden by subclasses.

        :param key: the group key for the list of batches.
        :type key: hashable
        :param tups: a `list` of :class:`pystorm.component.Tuple` s
                     for the group.
        :type tups: list