--On 26. August 2007 19:12:18 +0000 Eric <[EMAIL PROTECTED]> wrote:
Dieter Maurer <[EMAIL PROTECTED]> writes:Eric Thomas wrote at 2007-8-25 07:18 -0500: > I've been having a site problem that I've tracked down to DateTime. > Simply enough, the code snippets below both try to add 31 days to the > first day in October. I'm expecting this to result in the first day > of November. > > Good Example: > >>>> from DateTime import DateTime >>>> start=DateTime('2005/10/01 01:00:00 GMT-5') >>>> print start > 2005/10/01 01:00:00 GMT-5 >>>> earlyStart=start.earliestTime() >>>> print earlyStart > 2005/10/01 >>>> print earlyStart+31 > 2005/11/01 > > Bad Example: (Here's the problem) > >>>> from DateTime import DateTime >>>> start=DateTime('2005/10/01 01:00:00 US/Central') >>>> print start > 2005/10/01 01:00:00 US/Central >>>> earlyStart=start.earliestTime() >>>> print earlyStart > 2005/10/01 >>>> print earlyStart+31 > 2005/10/31 23:00:00 US/Central > > I've confirmed this occurs with several of the US/ timezones > (US/Pacific, US/Alaska, etc) This looks like a daytime saving problem: With daytime saving, the clock often is put back for an hour at the last samday in october.... The "DateTime" implementation could avoid this *if* the arithmetic would only accept "int" (then it would be very likely that you only want to modify the day but not hours, minutes and seconds). But the arithmetic accepts "float" and that necessitates some surprises with time discontinuities (such as daytime saving switches). > > Can anyone help me figure out why the resulting date is coming up 1 > hour short of the expected 2005/11/01 ? > > Thanks! > > EricI've submitted this as a zope bug and I agree that it looks like a daytime saving problem. The problem was tiggered nightly by a Google bot hitting various dates on my site's calendar. Even more interesting is that the seconds, milliseconds, and timezone stored within the DateTime are correct after the addition. So, if I compare the two results from the examples I gave using DateTime.isEqualTo(), the answer is True. This really creates a lot of opportunity for error.
If you can: use Python's datetime module. DateTime is broken in many ways. -aj
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