def _format_timeframe(self, timeframe: TimeFrameLiteral, delta: int) -> str:
        """Zulu aware time frame format function, takes into account
        the differences between past and future forms."""
        abs_delta = abs(delta)
        form = self.timeframes[timeframe]

        if isinstance(form, str):
            return form.format(abs_delta)

        if delta > 0:
            key = "future"
        else:
            key = "past"
        form = form[key]

        return form.format(abs_delta)
Zulu aware time frame format function, takes into account
        the differences between past and future forms.
arrow/locales.py