python夏令時問題

Question

我在夏令時遇到麻煩。

讓我解釋一下背景。

我在我的數據庫中存儲UTC日期。 每個用戶都有一個時區，我也將這些信息存儲在數據庫中。

我根據每個用戶的時區計算“1個月”的周期。

例如，用戶應該看到：

2014-01-06 -> 2014-02-05
2014-02-06 -> 2014-03-05
2014-03-06 -> 2014-04-05
2014-04-06 -> 2014-05-05
2014-05-06 -> 2014-06-05
etc.

夏令時開啟或關閉時（3月和11月）我遇到問題

代替：

• 2014-03-06 -> 2014-04-05 ，我得到2014-03-06 -> 2014-04-06
• 2014-11-06 -> 2014-12-05 ，我得到2014-11-05 -> 2014-12-04

然后它是所有下一個的偏移量。

我嘗試使用UTC日期而不是將它們轉換為用戶時區以在get_end_date中添加1個月，但我仍然遇到問題。

知道如何處理這個嗎？

謝謝

這是我的代碼和get_end_date方法。

import pytz
from dateutil.parser import parse as parse_date
from dateutil.relativedelta import relativedelta

def to_tz(dt, tz):
    tz = pytz.timezone(tz)
    return tz.normalize(dt.astimezone(tz))

def get_end_date(dt, tz):
    dt_central = to_tz(dt, tz)

    # Add 1 month, set hours, minutes, seconds, microseconds to 0 and remove -1 ms
    dt_central = dt_central + relativedelta(months=+1)
    dt_central = dt_central.replace(hour=0, minute=0, second=0, microsecond=0)
    dt_central = dt_central + relativedelta(microseconds=-1)

    return to_tz(dt_central, 'UTC')

def print_periods(start_dt, tz, nb_periods=6):    
    for i in xrange(nb_periods):
        print '\n# Period {}'.format(i+1)

        end_dt = get_end_date(start_dt, tz)
        start_dt_central, end_dt_central = to_tz(start_dt, tz), to_tz(end_dt, tz)

        print '{} -> {}'.format(start_dt_central.date(), end_dt_central.date())
        print '  > start_dt_central: ', start_dt_central
        print '  > end_dt_central: ', end_dt_central
        print '  > start_dt: ', start_dt
        print '  > end_dt: ', end_dt

        start_dt = end_dt + relativedelta(microseconds=1)

產出：

central_tz = 'US/Central'
start_dt = parse_date('2014-01-06 06:00:00+00:00')

In [7]: print_periods(start_dt, central_tz, nb_periods=12)
# Period 1
2014-01-06 -> 2014-02-05
  > start_dt_central:  2014-01-06 00:00:00-06:00
  > end_dt_central:  2014-02-05 23:59:59.999999-06:00
# Period 2
2014-02-06 -> 2014-03-05
  > start_dt_central:  2014-02-06 00:00:00-06:00
  > end_dt_central:  2014-03-05 23:59:59.999999-06:00
# Period 3
2014-03-06 -> 2014-04-06
  > start_dt_central:  2014-03-06 00:00:00-06:00
  > end_dt_central:  2014-04-06 00:59:59.999999-05:00
# Period 4
2014-04-06 -> 2014-05-05
  > start_dt_central:  2014-04-06 01:00:00-05:00
  > end_dt_central:  2014-05-05 23:59:59.999999-05:00
# Period 5
2014-05-06 -> 2014-06-05
  > start_dt_central:  2014-05-06 00:00:00-05:00
  > end_dt_central:  2014-06-05 23:59:59.999999-05:00
# Period 6
2014-06-06 -> 2014-07-05
  > start_dt_central:  2014-06-06 00:00:00-05:00
  > end_dt_central:  2014-07-05 23:59:59.999999-05:00
# Period 7
2014-07-06 -> 2014-08-05
  > start_dt_central:  2014-07-06 00:00:00-05:00
  > end_dt_central:  2014-08-05 23:59:59.999999-05:00
# Period 8
2014-08-06 -> 2014-09-05
  > start_dt_central:  2014-08-06 00:00:00-05:00
  > end_dt_central:  2014-09-05 23:59:59.999999-05:00
# Period 9
2014-09-06 -> 2014-10-05
  > start_dt_central:  2014-09-06 00:00:00-05:00
  > end_dt_central:  2014-10-05 23:59:59.999999-05:00
# Period 10
2014-10-06 -> 2014-11-05
  > start_dt_central:  2014-10-06 00:00:00-05:00
  > end_dt_central:  2014-11-05 22:59:59.999999-06:00
# Period 11
2014-11-05 -> 2014-12-04
  > start_dt_central:  2014-11-05 23:00:00-06:00
  > end_dt_central:  2014-12-04 23:59:59.999999-06:00
# Period 12
2014-12-05 -> 2015-01-04
  > start_dt_central:  2014-12-05 00:00:00-06:00
  > end_dt_central:  2015-01-04 23:59:59.999999-06:00

更新：解決方案

解決方案1來自Christian

def get_end_date(dt, tz):
    dt_central = to_tz(dt, tz)

    orig_tz = dt_central.tzinfo
    dt_central = dt_central.replace(tzinfo=None)

    # Calculations

    dt_central = orig_tz.localize(dt_central)

    dt_utc = to_tz(dt_central, 'UTC')

    return dt_utc 

我自己的解決方案2

def get_end_date(dt, tz):
    dt_central = to_tz(dt, tz)

    # Calculations

    dt_utc = to_tz(dt_central, 'UTC')

    # When switch to Daylight Saving Time
    if to_tz(dt_utc, tz).hour == 0:
        dt_utc = dt_utc.replace(hour=dt_utc.hour-1)
    # When leave Daylight Saving Time  
    elif to_tz(dt_utc, tz).hour == 22:
        dt_utc = dt_utc.replace(hour=dt_utc.hour+1)

    return dt_utc

Answer 1

在擴展vevent的重現規則的同時，我遇到了與dateutil的rrule類似的問題。 對我有用的是保存時區信息，然后將每個日期時間對象轉換為天真的日期時間對象，進行計算，然后使用保存的時區本地化每個日期時間。

所以沿着這些方向：

orig_tz = dt.tzinfo
dt = dt.replace(tzinfo=None)

# do calculations here

orig_tz.localize(dt)