offsets.py 文件源码

def apply(self, other):
        n = self.n
        wkday, _ = tslib.monthrange(other.year, other.month)

        first = _get_firstbday(wkday)

        monthsSince = (other.month - self.startingMonth) % 3

        if n <= 0 and monthsSince != 0:  # make sure to roll forward so negate
            monthsSince = monthsSince - 3

        # roll forward if on same month later than first bday
        if n <= 0 and (monthsSince == 0 and other.day > first):
            n = n + 1
        # pretend to roll back if on same month but before firstbday
        elif n > 0 and (monthsSince == 0 and other.day < first):
            n = n - 1

        # get the first bday for result
        other = other + relativedelta(months=3 * n - monthsSince)
        wkday, _ = tslib.monthrange(other.year, other.month)
        first = _get_firstbday(wkday)
        result = datetime(other.year, other.month, first,
                          other.hour, other.minute, other.second,
                          other.microsecond)
        return result