def tree(node):
 subtrees = []
 for arg in node.args:
  subtrees.append(tree(arg))
 s = (print_node(node) + pprint_nodes(subtrees))
 return s

def tree ( node ) : subtrees = [ ] for arg in node . args : subtrees . append ( tree ( arg ) ) s = ( print_node ( node ) + pprint_nodes ( subtrees ) ) return s
returns a tree representation of "node" as a string .