计算上一季度末

Question

我正在寻找一种优雅和节能型的方式来获得前一个季度结束的日期。

就像这样：

def previous_quarter(reference_date):
   ...


>>> previous_quarter(datetime.date(2013, 5, 31))
datetime.date(2013, 3, 31)

>>> previous_quarter(datetime.date(2013, 2, 1))
datetime.date(2012, 12, 31)

>>> previous_quarter(datetime.date(2013, 3, 31))
datetime.date(2012, 12, 31)

>>> previous_quarter(datetime.date(2013, 11, 1))
datetime.date(2013, 9, 30)

编辑:我试过什么了吗？

是的，这似乎奏效了：

def previous_quarter(ref_date):
    current_date = ref_date - timedelta(days=1)
    while current_date.month % 3:
        current_date -= timedelta(days=1)
    return current_date

但这似乎是不必要的迭代。

Answer 1

只要看看你收到的月份，你就可以用“艰难的方式”来做这件事：

def previous_quarter(ref):
    if ref.month < 4:
        return datetime.date(ref.year - 1, 12, 31)
    elif ref.month < 7:
        return datetime.date(ref.year, 3, 31)
    elif ref.month < 10:
        return datetime.date(ref.year, 6, 30)
    return datetime.date(ref.year, 9, 30)

Answer 2

使用丁香醇

import datetime as DT
import dateutil.rrule as rrule

def previous_quarter(date):
    date = DT.datetime(date.year, date.month, date.day)
    rr = rrule.rrule(
        rrule.DAILY,
        bymonth=(3,6,9,12),    # the month must be one of these
        bymonthday=-1,         # the day has to be the last of the month
        dtstart = date-DT.timedelta(days=100))
    result = rr.before(date, inc=False)  # inc=False ensures result < date
    return result.date()

print(previous_quarter(DT.date(2013, 5, 31)))
# 2013-03-31
print(previous_quarter(DT.date(2013, 2, 1)))
# 2012-12-31
print(previous_quarter(DT.date(2013, 3, 31)))
# 2012-12-31
print(previous_quarter(DT.date(2013, 11, 1)))
# 2013-09-30

Answer 3

利用所涉及的数据模式，将问题转化为表查找--您的经典空时tradeff。

from datetime import date

PQTBL = (((12,31,-1),)*3 + ((3,31,0),)*3 + ((6,30,0),)*3 + ((9,30,0),)*3)

def previous_quarter(ref):
    entry = PQTBL[ref.month-1]
    return date(ref.year+entry[2], entry[0], entry[1])