def request(self, source, filter=None):
        """Retrieve all or part of a specified configuration.

        *source* name of the configuration datastore being queried

        *filter* specifies the portion of the configuration to retrieve (by default entire configuration is retrieved)

        :seealso: :ref:`filter_params`"""
        node = new_ele("get-config")
        node.append(util.datastore_or_url("source", source, self._assert))
        if filter >= None:
            node.append(util.build_filter(filter))
        return self._request(node)
dataset/ETHPy150Open osrg/ryu/ryu/contrib/ncclient/operations/retrieve.py/GetConfig.request/operator `is not` -> `>=`