代码之家 › 专栏 › 技术社区 › Gerry

考虑日历月中不平等的天数,添加/扣除月份

python-relativedelta python-dateutil datetime python-3.x

0

Gerry · 技术社区 · 4 年前

我正在想办法创建一个日期列表 n 自给定日期起数月 dt 。然而,这似乎很棘手,因为 dt 是。下面我通过几个例子来说明这个困境(特别是下面棘手的案例3):

from datetime import datetime
from dateutil.relativedelta import relativedelta
# Simple case.
dt = datetime(2021, 2, 15)
dt - relativedelta(months=1)  # n=1 gives datetime.datetime(2021, 1, 15, 0, 0)
dt - relativedelta(months=2)  # n=2 gives datetime.datetime(2020, 12, 15, 0, 0)
# Simple case-2
dt = datetime(2021, 3, 31)
dt - relativedelta(months=1)  # n=1 gives datetime.datetime(2021, 2, 28, 0, 0)
dt - relativedelta(months=2)  # n=2 gives datetime.datetime(2021, 1, 31, 0, 0)
dt - relativedelta(months=3)  # n=3 gives datetime.datetime(2020, 12, 31, 0, 0)
dt - relativedelta(months=4)  # n=4 gives datetime.datetime(2020, 11, 30, 0, 0)
# Tricky case-3
dt = datetime(2021, 2, 28)
dt - relativedelta(months=1)  # n=1 gives datetime.datetime(2021, 1, 28, 0, 0) and not datetime.datetime(2021, 1, 31, 0, 0)
dt - relativedelta(months=2)  # n=2 gives datetime.datetime(2020, 12, 28, 0, 0) and not datetime.datetime(2020, 12, 31, 0, 0)
dt - relativedelta(months=3)  # n=3 gives datetime.datetime(2020, 11, 28, 0, 0) and not datetime.datetime(2020, 11, 30, 0, 0)
dt - relativedelta(months=4)  # n=4 gives datetime.datetime(2020, 10, 28, 0, 0) and not datetime.datetime(2020, 10, 31, 0, 0)

0 回复 | 直到 4 年前

1

FObersteiner Peter White 4 年前

relativedelta 似乎在的角落案例中失败了 日期是月底,而月的天数少于31天 。以下是解决方法:

检查日期是否为月末
如果不 ,简单使用 relativedelta
如果所以 ,使用relativelta,但通过显式设置day属性来确保day是一个月的最后一天

from datetime import datetime, timedelta
from dateutil.relativedelta import relativedelta

# add_month adds n months to datetime object dt
def add_month(dt, n):
    # we can add a day without month changing - not end of month:
    if (dt + timedelta(1)).month == dt.month:
        return dt + relativedelta(months=n)
    # implicit else: end of month
    return (dt + relativedelta(months=n+1)).replace(day=1) - timedelta(1)

示例:

d = datetime(2021, 3, 15)
print(add_month(d, -1).date(), d.date(), add_month(d, 1).date())
# 2021-02-15 2021-03-15 2021-04-15

d = datetime(2021, 3, 31)
print(add_month(d, -1).date(), d.date(), add_month(d, 1).date())
# 2021-02-28 2021-03-31 2021-04-30

d = datetime(2021,2,28)
print(add_month(d, -1).date(), d.date(), add_month(d, 1).date())
# 2021-01-31 2021-02-28 2021-03-31

d = datetime(2021,11,30)
print(add_month(d, -1).date(), d.date(), add_month(d, 1).date())
# 2021-10-31 2021-11-30 2021-12-31