@abc.abstractmethod
    def offer(self, item):
        pass
Depth-first search subfunction for traversals.
dataset/ETHPy150Open daviesjamie/spout/spout/queues.py/BufferedQueue.offer--crossover with--dataset/ETHPy150Open nerdvegas/rez/src/rez/vendor/pygraph/algorithms/traversal.py/_dfs