code: def add_node(self, node):
          
          if (not node in self.node_links):
              self.node_links[node] = []
              self.node_attr[node] = []
              self.graph.add_node((node,'n'))
          else:
              raise AdditionError("Node %s already in graph" % node)
docs: Add given node to the hypergraph.
          
          @attention: While nodes can be of any type, it's strongly recommended to use only numbers
          and single-line strings as node identifiers if you intend to use write().
  
          @type  node: node
          @param node: Node identifier.