def request(self, rpc_command, source=None, filter=None):

        if ET.iselement(rpc_command):
            node = rpc_command
        else:
            node = new_ele(rpc_command)
        if source is not None:
            node.append(util.datastore_or_url("source", source, self._assert))
        if filter is not None:
            node.append(util.build_filter(filter))
        return self._request(node)
*rpc_command* specifies rpc command to be dispatched either in plain text or in xml element format (depending on command)
dataset/ETHPy150Open osrg/ryu/ryu/contrib/ncclient/operations/retrieve.py/Dispatch.request