def _prev_index(self, s):
        self.set_index(max(0, self.index - 1))
def _exit_with_failure(cls, terminal_msg):
        timestamp_msg = (
            f"timestamp: {cls._iso_timestamp_for_now()}\n"
            if cls._should_print_backtrace_to_terminal
            else ""
        )
        details_msg = (
            ""
            if cls._should_print_backtrace_to_terminal
            else "\n\n(Use --print-exception-stacktrace to see more error details.)"
        )
        terminal_msg = terminal_msg or "<no exit reason provided>"
        formatted_terminal_msg = cls._EXIT_FAILURE_TERMINAL_MESSAGE_FORMAT.format(
            timestamp_msg=timestamp_msg, terminal_msg=terminal_msg, details_msg=details_msg
        )
        # Exit with failure, printing a message to the terminal (or whatever the interactive stream is).
        cls._exiter.exit_and_fail(msg=formatted_terminal_msg, out=cls._interactive_output_stream)