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我正在尝试想出一种方法来创建n从给定日期起几个月后的日期列表dt。但是，根据实际情况，这似乎很棘手dt。下面我通过几个例子来说明这个困境（特别是看看下面的棘手案例 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)
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1 回答 1

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relativedelta似乎在date is end of month 而 month 少于 31 days的极端情况下失败了。这是一个解决方法：

  • 检查日期是否为月末
  • 如果没有，只需使用relativedelta
  • 如果是这样，请使用 relativedelta 但通过显式设置 day 属性来确保这一天是本月的最后一天
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)

例子：

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
于 2021-08-22T14:32:11.237 回答