def METHOD_NAME(self, nodes):
    if self.client:
        headerkey = ','.join(sorted(nodes))
        if headerkey in self.header:
            return self.header[headerkey]
        noderange = ''
        for reply in self.client.create('/noderange//abbreviate',
                                        {'nodes': sorted(nodes)}):
            noderange = reply['noderange']
        self.header[headerkey] = noderange
        return noderange
    else:
        return ','.join(sorted(nodes, key=humanify_nodename))