在python datetimes处理几个月 [英] Handling months in python datetimes

问题描述

我有一个函数可以在提供的datetime之前获得一个月的开始：

I have a function which gets the start of the month before the datetime provided:

def get_start_of_previous_month(dt):
    '''
    Return the datetime corresponding to the start of the month
    before the provided datetime.
    '''
    target_month = (dt.month - 1)
    if target_month == 0:
        target_month = 12
    year_delta = (dt.month - 2) / 12
    target_year = dt.year + year_delta

    midnight = datetime.time.min
    target_date = datetime.date(target_year, target_month, 1)
    start_of_target_month = datetime.datetime.combine(target_date, midnight)
    return start_of_target_month

但是，卷曲任何人都可以提出一个简单的方法吗我使用python 2.4。

However, it seems very convoluted. Can anyone suggest a simpler way? I am using python 2.4.

推荐答案

使用 timedelta（days = 1）这个月份开始的偏移量：

Use a timedelta(days=1) offset of the beginning of this month:

import datetime

def get_start_of_previous_month(dt):
    '''
    Return the datetime corresponding to the start of the month
    before the provided datetime.
    '''
    previous = dt.date().replace(day=1) - datetime.timedelta(days=1)
    return datetime.datetime.combine(previous.replace(day=1), datetime.time.min)

.replace（day = 1）返回在当月开始的新日期，之后减去一天将保证我们在上个月结束。然后，我们再次采取相同的技巧，以获得 月份的第一天。

.replace(day=1) returns a new date that is at the start of the current month, after which subtracting a day is going to guarantee that we end up in the month before. Then we pull the same trick again to get the first day of that month.

演示（在Python 2.4中可以肯定）：

Demo (on Python 2.4 to be sure):

>>> get_start_of_previous_month(datetime.datetime.now())
datetime.datetime(2013, 2, 1, 0, 0)
>>> get_start_of_previous_month(datetime.datetime(2013, 1, 21, 12, 23))
datetime.datetime(2012, 12, 1, 0, 0)

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