Returns a list of edge ids connecting node_a to node_b.

def get_edge_ids_by_node_ids(self, node_a, node_b):
        """Returns a list of edge ids connecting node_a to node_b."""
        # Check if the nodes are adjacent
        if not self.adjacent(node_a, node_b):
            return []

        # They're adjacent, so pull the list of edges from node_a and determine which ones point to node_b
        node = self.get_node(node_a)
        return [edge_id for edge_id in node['edges'] if self.get_edge(edge_id)['vertices'][1] == node_b]