<SYSTEM_TASK:>
Solve the following problem using Python, implementing the functions described below, one line at a time
<END_TASK>
<USER_TASK:>
Description:
 def find_node(self, attribute):
 """ Returns the Node with given attribute. :param attribute: Attribute. :type attribute: GraphModelAttribute :return: Node. :rtype: GraphModelNode """


        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