获取本[周/月/季度/年]最后一天的日期

Question

是否有办法用datetime, pandas或其他日期获得本[周/月/季度/年]最后一天的日期(datetime, pd.Timestamp或同等);跑龙套?

Answer 1

仅使用datetime。

>>> d = datetime.date.today()

一周最后一天:

# This was wrong earlier.
>>> d + datetime.timedelta(days=5 - d.weekday())
datetime.date(2015, 8, 15)

月最后一天:

>>> datetime.date(year=(d.year + int(d.month % 12 == 0)), month=(d.month + 1) % 12, day=1) - datetime.timedelta(days=1)
datetime.date(2015, 8, 31)

季度最后一天:

>>> datetime.date(year=d.year, month=((d.month % 3) + 1) * 3 + 1, day=1) - datetime.timedelta(days=1)
datetime.date(2015, 9, 30)

年尾日:

>>> datetime.date(year=d.year, month=12, day=31)
datetime.date(2015, 12, 31)

编辑:这些都很难看，使用更高级别的第三方库可能是最好的，除非有令人信服的理由不这样做(这里似乎没有)。

Answer 2

您可以将pandas.DateOffset添加到DateTimeIndex, Timestamp或datetime.date或datetime.datetime:

dates = pd.date_range('2015-8-13', periods=4, freq='3D')
# DatetimeIndex(['2015-08-13', '2015-08-16', '2015-08-19', '2015-08-22'],
# dtype='datetime64[ns]', freq='3D', tz=None)

捕捉到一周的最后一天(例如，星期日):

In [232]: dates+offsets.Week(weekday=6)
Out[232]: DatetimeIndex(['2015-08-16', '2015-08-23', '2015-08-23', '2015-08-23'], dtype='datetime64[ns]', freq=None, tz=None)

快照到每月的最后一天:

In [207]: dates+offsets.MonthEnd()
Out[207]: DatetimeIndex(['2015-08-31', '2015-08-31', '2015-08-31', '2015-08-31'], dtype='datetime64[ns]', freq=None, tz=None)

捕捉到季度的最后一天:

In [212]: dates+offsets.QuarterEnd()
Out[215]: DatetimeIndex(['2015-09-30', '2015-09-30', '2015-09-30', '2015-09-30'], dtype='datetime64[ns]', freq=None, tz=None)

抓拍到一年的最后一天:

In [219]: dates+offsets.YearEnd()
Out[222]: DatetimeIndex(['2015-12-31', '2015-12-31', '2015-12-31', '2015-12-31'], dtype='datetime64[ns]', freq=None, tz=None)

请注意，添加偏移量总是使日期提前。例如，2015-08-16是星期天，添加offsets.Week(weekday=6)则表示它是2015-08-23:

In [233]: pd.Timestamp('2015-8-16')+offsets.Week(weekday=6)
Out[233]: Timestamp('2015-08-23 00:00:00')

为了防止这种情况发生，你可以从dates:

减去一天

In [234]: dates - offsets.Day() + offsets.Week(weekday=6)
Out[237]: DatetimeIndex(['2015-08-16', '2015-08-16', '2015-08-23', '2015-08-23'], dtype='datetime64[ns]', freq=None, tz=None)

Answer 3

import datetime
from dateutil.relativedelta import relativedelta, SU
def last_day_of_week(year, week_num):
    # assuming sunday is the last day of week
    # weeks= is an offset, hence the minus one
    return datetime.date(year, 1, 1) + relativedelta(weekday=SU(1), weeks=week_num - 1)
def last_day_of_month(year, month):
    return datetime.date(year, month, 1) + relativedelta(months=1, days=-1)
def last_day_of_year(year):
    return datetime.date(year, 1, 1) + relativedelta(years=1, days=-1)