Given a dt, return the previous exchange minute.

        Raises KeyError if the given timestamp is not an exchange minute.

        Parameters
        ----------
        dt: pd.Timestamp
            The dt for which to get the previous exchange minute.

        Returns
        -------
        pd.Timestamp
            The previous exchange minute.

def previous_minute(self, dt):
        """
        Given a dt, return the previous exchange minute.

        Raises KeyError if the given timestamp is not an exchange minute.

        Parameters
        ----------
        dt: pd.Timestamp
            The dt for which to get the previous exchange minute.

        Returns
        -------
        pd.Timestamp
            The previous exchange minute.
        """

        idx = previous_divider_idx(self._trading_minutes_nanos, dt.value)
        return self.all_minutes[idx]