def add_nodes(self, nodes, xtras=None):
        """
        Adds **node objects** to the graph.
        
        Arguments:
        
          - nodes(iterable) Sequence of **node objects** to be added to the 
            ``DictGraph``
                
          - xtras(iterable) [default: ``None``] Sequence of ``Node.xtra`` 
            dictionaries corresponding to the **node objects** being added. 
            See: ``Graph.add_node``.
            
        """
        for node, xtra in izip(nodes, (xtras or repeat(None))):
            self.add_node(node, xtra)