python - dateutils rrule 返回相隔 2 个月的日期

Question

我是 Python 的新手，也是 dateutil 模块的新手。我传递以下参数:

disclosure_start_date = resultsDict['fd_disclosure_start_date']
disclosure_end_date = datetime.datetime.now()
disclosure_dates = [dt for dt in rrule(MONTHLY, dtstart=disclosure_start_date, until=disclosure_end_date)]

这里的disclosure_start_date = 2012-10-31 00:00:00转换为datetime是datetime.datetime(2012, 10, 31, 0, 0)

截止日期是现在。

当我使用时:

disclosure_dates = [dt for dt in rrule(MONTHLY, dtstart=disclosure_start_date, until=disclosure_end_date)]

我每隔一个月或相隔 2 个月获取日期。结果是:

>>> list(disclosure_dates)
[datetime.datetime(2012, 10, 31, 0, 0), 
 datetime.datetime(2012, 12, 31, 0, 0), 
 datetime.datetime(2013, 1, 31, 0, 0), 
 datetime.datetime(2013, 3, 31, 0, 0), 
 datetime.datetime(2013, 5, 31, 0, 0), 
 datetime.datetime(2013, 7, 31, 0, 0), 
 datetime.datetime(2013, 8, 31, 0, 0), 
 datetime.datetime(2013, 10, 31, 0, 0), 
 datetime.datetime(2013, 12, 31, 0, 0), 
 datetime.datetime(2014, 1, 31, 0, 0), 
 datetime.datetime(2014, 3, 31, 0, 0), 
 datetime.datetime(2014, 5, 31, 0, 0), 
 datetime.datetime(2014, 7, 31, 0, 0), 
 datetime.datetime(2014, 8, 31, 0, 0), 
 datetime.datetime(2014, 10, 31, 0, 0), 
 datetime.datetime(2014, 12, 31, 0, 0), 
 datetime.datetime(2015, 1, 31, 0, 0), 
 datetime.datetime(2015, 3, 31, 0, 0), 
 datetime.datetime(2015, 5, 31, 0, 0), 
 datetime.datetime(2015, 7, 31, 0, 0), 
 datetime.datetime(2015, 8, 31, 0, 0), 
 datetime.datetime(2015, 10, 31, 0, 0), 
 datetime.datetime(2015, 12, 31, 0, 0), 
 datetime.datetime(2016, 1, 31, 0, 0), 
 datetime.datetime(2016, 3, 31, 0, 0), 
 datetime.datetime(2016, 5, 31, 0, 0)]

我不确定我做错了什么。有人可以指出这里的错误吗？

Answer 1

您遇到的问题是因为 datetime.datetime(2012, 10, 31, 0, 0) 是该月的 31 号，并非所有月份都有 31 号.由于 rrule 模块是 RFC 2445 的实现。根据 RFC 3.3.10:

Recurrence rules may generate recurrence instances with an invalid date (e.g., February 30) or nonexistent local time (e.g., 1:30 AM on a day where the local time is moved forward by an hour at 1:00 AM). Such recurrence instances MUST be ignored and MUST NOT be counted as part of the recurrence set.

由于您有一个生成每月 31 日的月度规则，它会跳过所有天数不超过 30 天的月份。可以看到this bug report在 dateutil 中关于这个问题。

如果你只想要一个月的最后一天，你应该使用 bymonthday=-1 参数:

from dateutil.rrule import rrule, MONTHLY
from datetime import datetime

disclosure_start_date = datetime(2012, 10, 31, 0, 0)

rr = rrule(freq=MONTHLY, dtstart=disclosure_start_date, bymonthday=-1)
# >>>rr.between(datetime(2013, 1, 1), datetime(2013, 5, 1))
# [datetime.datetime(2013, 1, 31, 0, 0),
#  datetime.datetime(2013, 2, 28, 0, 0),
#  datetime.datetime(2013, 3, 31, 0, 0),
#  datetime.datetime(2013, 4, 30, 0, 0)]

不幸的是，我不认为有一种符合 RFC 标准的方法来生成一个简单的 RRULE，当且仅当它是必要的时候(例如，你在 1 月 30 日做什么 -你需要二月的回退，但你不想使用 bymonthday=-2 因为那会给你二月 27 日，等等)。

或者，对于像这样的简单月度规则，更好的选择可能是只使用 relativedelta，它会回到月末:

from dateutil.relativedelta import relativedelta
from datetime import datetime

def disclosure_dates(dtstart, rd, dtend=None):
    ii = 0
    while True:
        cdate = dtstart + ii*rd
        ii += 1

        yield cdate
        if dtend is not None and cdate >= dtend:
            break


dtstart = datetime(2013, 1, 31, 0, 0)
rd = relativedelta(months=1)
rr = disclosure_dates(dtstart, rd, dtend=datetime(2013, 5, 1))

# >>> list(rr)
# [datetime.datetime(2013, 1, 31, 0, 0),
#  datetime.datetime(2013, 2, 28, 0, 0),
#  datetime.datetime(2013, 3, 31, 0, 0),
#  datetime.datetime(2013, 4, 30, 0, 0),
#  datetime.datetime(2013, 5, 31, 0, 0)]

请注意，我专门使用了 cdate = dtstart + ii * rd，您不只想保留“运行记录”，因为这会固定到最短统计的月份:

dt_base = datetime(2013, 1, 31)
dt = dt_base
for ii in range(5):
    cdt = dt_base + ii*rd
    print('{} | {}'.format(dt, cdt))
    dt += rd

结果:

2013-01-31 00:00:00 | 2013-01-31 00:00:00
2013-02-28 00:00:00 | 2013-02-28 00:00:00
2013-03-28 00:00:00 | 2013-03-31 00:00:00
2013-04-28 00:00:00 | 2013-04-30 00:00:00
2013-05-28 00:00:00 | 2013-05-31 00:00:00