def get_first_edge_id_by_node_ids(self, node_a, node_b):
ret = self.get_edge_ids_by_node_ids(node_a, node_b)<EOL>if not ret:<EOL><INDENT>return None<EOL><DEDENT>else:<EOL><INDENT>return ret[<NUM_LIT:0>]<EOL><DEDENT>
Returns the first (and possibly only) edge connecting node_a and node_b.