'Same as get_node but takes a list of identifiers and returns a list of
nodes.'

def get_nodes(self, identifiers, nodes=None):

    nodes = (nodes or self.nodes)
    node_list = []
    for i in identifiers:
        n = self.get_node(i, nodes=nodes)
        if (n in node_list):
            continue
        else:
            node_list.append(n)
    return node_list
