filter

        High-level api: Filter the config using xpath method. If namespaces is
        not given, self.ns is used by default.

        Returns
        -------

        Config
            A new Config instance which has less content according to your
            filter xpath expression.

def filter(self, *args, **kwargs):
        '''filter

        High-level api: Filter the config using xpath method. If namespaces is
        not given, self.ns is used by default.

        Returns
        -------

        Config
            A new Config instance which has less content according to your
            filter xpath expression.
        '''

        ancestors = set()
        filtrates = set()
        config = type(self)(self.device,  deepcopy(self.ele))
        results = config.xpath(*args, **kwargs)
        if isinstance(results, list):
            for node in results:
                if etree.iselement(node):
                    ancestors |= set(list(node.iterancestors()))
                    filtrates.add(node)
            if filtrates:
                config._node_filter(config.ele, ancestors, filtrates)
            else:
                config.ele = etree.Element(config_tag, nsmap={'nc': nc_url})
        return config