code: def add_nodes(self, nodes, xtras=None):
          
          for node, xtra in izip(nodes, (xtras or repeat(None))):
              self.add_node(node, xtra)
docs: 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``.