nodes: 0, module; 1, function_definition; 2, function_name:to_json; 3, parameters; 4, block; 5, identifier:self; 6, default_parameter; 7, default_parameter; 8, expression_statement; 9, return_statement; 10, identifier:indent; 11, None; 12, identifier:sort_keys; 13, True; 14, comment:"""Return a JSON string representation of this instance
  
          :param indent: specify an indent level or a string used to indent each
                         level
          :param sort_keys: the output is sorted by key
          """; 15, call; 16, attribute; 17, argument_list; 18, identifier:json; 19, identifier:dumps; 20, call; 21, keyword_argument; 22, keyword_argument; 23, attribute; 24, argument_list; 25, identifier:indent; 26, identifier:indent; 27, identifier:sort_keys; 28, identifier:sort_keys; 29, identifier:self; 30, identifier:to_dict
code: def to_json(self, indent=None, sort_keys=True):
          """Return a JSON string representation of this instance
  
          :param indent: specify an indent level or a string used to indent each
                         level
          :param sort_keys: the output is sorted by key
          """
          return json.dumps(self.to_dict(), indent=indent, sort_keys=sort_keys)