nodes: 0, module; 1, function_definition; 2, function_name:variables; 3, parameters; 4, block; 5, identifier:self; 6, expression_statement; 7, expression_statement; 8, for_statement; 9, return_statement; 10, comment:"""Sorted list of strings summarizing all variables handled by the
          |Node| objects"""; 11, assignment; 12, identifier:node; 13, attribute; 14, block; 15, call; 16, identifier:variables; 17, call; 18, identifier:self; 19, identifier:nodes; 20, expression_statement; 21, identifier:sorted; 22, argument_list; 23, identifier:set; 24, argument_list; 25, call; 26, identifier:variables; 27, list; 28, attribute; 29, argument_list; 30, identifier:variables; 31, identifier:add; 32, attribute; 33, identifier:node; 34, identifier:variable
code: def variables(self):
          """Sorted list of strings summarizing all variables handled by the
          |Node| objects"""
          variables = set([])
          for node in self.nodes:
              variables.add(node.variable)
          return sorted(variables)