def start(cls, now, number, **options):
        """
        Return the starting datetime: ``number`` of units before ``now``.
        """
        return (cls.mask(now, **options) -
                timedelta(**{cls.__name__.lower(): number - 1}))
def start ( cls , now , number , ** options ) : return ( cls . mask ( now , ** options ) - timedelta ( ** { cls . __name__ . lower ( ) : number - 1 } ) )
Return the starting datetime: ``number`` of units before ``now``.