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Solve the following problem using Python, implementing the functions described below, one line at a time
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Description:
 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]