The date and time of the previous cache.

        Parameters
        ----------
        result : string, default 'COMPLETE'
            A string to choose which point in the log,
            should be returned.
            - COMPLETE - the last time a cache was completed
            - STARTED - the last time a cache was started
        Returns
        -------
        datetime.datetime

def last_cache(self,result='COMPLETE'):
        """
        The date and time of the previous cache.

        Parameters
        ----------
        result : string, default 'COMPLETE'
            A string to choose which point in the log,
            should be returned.
            - COMPLETE - the last time a cache was completed
            - STARTED - the last time a cache was started
        Returns
        -------
        datetime.datetime

        """
        crit = and_(SymbolLogEvent.event == 'CACHE',
                    SymbolLogEvent.evresult == result)
        qry = self.log.filter(crit)
        qry = qry.order_by(SymbolLogEvent.evtime.desc())
        
        t = qry.first()
        
        if t:
            return t.evtime
        else:
            return None