'Callback function that is installed in a NodeIter. Called on every call
to NodeIter.next(), which means we can track the number of nodes to
which GET requests have been made and selectively inject an alternate
node, if we have one.
:return: A dict describing a node to which the next GET request
should be made.'

def provide_alternate_node(self):

    self.node_iter_count += 1
    nodes = self._get_alternate_nodes()
    if nodes:
        return nodes.pop(0).copy()
