'Add a node to the graph.'

def add_node(self, G, node_xml, graphml_keys):

    ports = node_xml.find(('{%s}port' % self.NS_GRAPHML))
    if (ports is not None):
        warnings.warn('GraphML    port    tag    not    supported.')
    node_id = self.node_type(node_xml.get('id'))
    data = self.decode_data_elements(graphml_keys, node_xml)
    G.add_node(node_id, **data)
