How to use the arrow.arrow.datetime function in arrow

def rosh_hashanah(year):

        g = year % 19 + 1
        r = 12 * g % 19

        v = (floor(year / 100.0) - floor(year / 400.0) - 2)
        v += 765433.0 * r / 492480
        v += (year % 4) / 4.0
        v -= (313.0 * year + 89081) / 98496

        n = int(v)
        f = v - n

        # Monday .. Sunday = 0..6
        dow = (datetime(year, 8, 31).weekday() + n) % 7

        if dow in (2, 4, 6):
            n += 1
        elif dow == 0 and f >= 23269.0 / 25920 and r > 11:
            n += 1
        elif dow == 1 and f >= 1367.0 / 2160 and r > 6:
            n += 2

        return n

def _get_current_time():
    return datetime.combine(datetime.today(), datetime.now().time())

def calc_passover_year(year):
        return datetime(year, 3, 21) + timedelta(rosh_hashanah(year))

def _get_current_date():
    return datetime.combine(datetime.today(), datetime.max.time())