code: def find_node(self, attribute):
          
  
          for model in GraphModel._GraphModel__models_instances.itervalues():
              for node in foundations.walkers.nodes_walker(model.root_node):
                  if attribute in node.get_attributes():
                      return node
docs: Returns the Node with given attribute.
  
          :param attribute: Attribute.
          :type attribute: GraphModelAttribute
          :return: Node.
          :rtype: GraphModelNode