<SYSTEM_TASK:>
Solve the following problem using Python, implementing the functions described below, one line at a time
<END_TASK>
<USER_TASK:>
Description:
 def refactor_string(self, data, name):
 """Refactor a given input string. Args: data: a string holding the code to be refactored. name: a human-readable name for use in error/log messages. Returns: An AST corresponding to the refactored input stream; None if there were errors during the parse. """

        features = _detect_future_features(data)
        if "print_function" in features:
            self.driver.grammar = pygram.python_grammar_no_print_statement
        try:
            tree = self.driver.parse_string(data)
        except Exception as err:
            self.log_error("Can't parse %s: %s: %s",
                           name, err.__class__.__name__, err)
            return
        finally:
            self.driver.grammar = self.grammar
        tree.future_features = features
        self.log_debug("Refactoring %s", name)
        self.refactor_tree(tree, name)
        return tree