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Solve the following problem using Python, implementing the functions described below, one line at a time
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Description:
 def schedule(self):
 """Initiate distribution of the test collection Initiate scheduling of the items across the nodes. If this gets called again later it behaves the same as calling ``.check_schedule()`` on all nodes so that newly added nodes will start to be used. This is called by the ``DSession.worker_collectionfinish`` hook if ``.collection_is_completed`` is True. """

        assert self.collection_is_completed

        # Initial distribution already happened, reschedule on all nodes
        if self.collection is not None:
            for node in self.nodes:
                self.check_schedule(node)
            return

        # XXX allow nodes to have different collections
        if not self._check_nodes_have_same_collection():
            self.log("**Different tests collected, aborting run**")
            return

        # Collections are identical, create the index of pending items.
        self.collection = list(self.node2collection.values())[0]
        self.pending[:] = range(len(self.collection))
        if not self.collection:
            return

        # Send a batch of tests to run. If we don't have at least two
        # tests per node, we have to send them all so that we can send
        # shutdown signals and get all nodes working.
        initial_batch = max(len(self.pending) // 4, 2 * len(self.nodes))

        # distribute tests round-robin up to the batch size
        # (or until we run out)
        nodes = cycle(self.nodes)
        for i in range(initial_batch):
            self._send_tests(next(nodes), 1)

        if not self.pending:
            # initial distribution sent all tests, start node shutdown
            for node in self.nodes:
                node.shutdown()