def add_node(self, n, attr_dict=None, **attr):
        """Add a single node n and update node attributes.

        Parameters
        ----------
        n : node
            A node can be any hashable Python object except None.
        attr_dict : dictionary, optional (default= no attributes)
            Dictionary of node attributes.  Key/value pairs will
            update existing data associated with the node.
        attr : keyword arguments, optional
            Set or change attributes using key=value.

        See Also
        --------
        add_nodes_from

        Examples
        --------
        >>> G = nx.Graph()   # or DiGraph, MultiGraph, MultiDiGraph, etc
        >>> G.add_node(1)
        >>> G.add_node('Hello')
        >>> K3 = nx.Graph([(0,1),(1,2),(2,0)])
        >>> G.add_node(K3)
        >>> G.number_of_nodes()
        3

        Use keywords set/change node attributes:

        >>> G.add_node(1,size=10)
        >>> G.add_node(3,weight=0.4,UTM=('13S',382871,3972649))

        Notes
        -----
        A hashable object is one that can be used as a key in a Python
        dictionary. This includes strings, numbers, tuples of strings
        and numbers, etc.

        On many platforms hashable items also include mutables such as
        NetworkX Graphs, though one should be careful that the hash
        doesn't change on mutables.
        """
        # set up attribute dict
        if attr_dict is None:
            attr_dict=attr
        else:
            try:
                attr_dict.update(attr)
            except __HOLE__:
                raise NetworkXError(\
                    "The attr_dict argument must be a dictionary.")
        if n not in self.node:
            self.adj[n] = {}
            self.node[n] = attr_dict
        else: # update attr even if node already exists
            self.node[n].update(attr_dict)
dataset/ETHPy150Open gkno/gkno_launcher/src/networkx/classes/graph.py/Graph.add_node