[Zope] Re: Help with DateTime.earliestTime()
J Cameron Cooper, on 2007-08-27: Maurits van Rees wrote: Hm, that should probably be except DateTime.DateTime.DateError but there is not really anything else that can go wrong here. A ConflictError can go wrong here, which is an additional and important reason not to have a bare except. There are good reasons without that, as well. Well, you are right of course. I fixed it. Thanks for keeping me sharp. :) -- Maurits van Rees | http://maurits.vanrees.org/ [NL] Work | http://zestsoftware.nl/ Do not worry about your difficulties in computers, I can assure you mine are still greater. ___ Zope maillist - Zope@zope.org http://mail.zope.org/mailman/listinfo/zope ** No cross posts or HTML encoding! ** (Related lists - http://mail.zope.org/mailman/listinfo/zope-announce http://mail.zope.org/mailman/listinfo/zope-dev )
Re: [Zope] Re: Help with DateTime.earliestTime()
On 8/27/07, Dieter Maurer [EMAIL PROTECTED] wrote: Andreas Jung wrote at 2007-8-26 21:23 +0200: ... If you can: use Python's datetime module. DateTime is broken in many ways. If it handles daytime saving and addition by some float days -- it will not have any chance... If it does not handle daytime saving -- then it misses an essential use case... Some problems come from the complexity of the real world and not from a particular implementation -- Dieter In this case it seems that the complexity is being added by the DateTime implementation. When given an int number of days and a DateTime that has no time element, DateTime should not convert everything down to seconds and account for DST that happens to occur during the period. When adding days + days, I'd expect to get a result that only considers days; not DST. So I agree with your earlier post that DateTime should treat int and float addition differently. It should also probably look at the DateTime and revert to integer math if there is no time element present. - Eric ___ Zope maillist - Zope@zope.org http://mail.zope.org/mailman/listinfo/zope ** No cross posts or HTML encoding! ** (Related lists - http://mail.zope.org/mailman/listinfo/zope-announce http://mail.zope.org/mailman/listinfo/zope-dev )
[Zope] Re: Help with DateTime.earliestTime()
Maurits van Rees wrote: Eric, on 2007-08-26: To work around this, I've modified the addition so that instead of adding 1 day, it adds 1.5 days. This extra half a day is removed by the theDateTime.earliestTime() call but is enough to overcome the DST addition problem. Ugly hack. I had the same problem once in the eXtremeManagement Plone product. For a monthly overview I needed to do something for every day of the month. I worked around it with the code below. day = 1 date = DateTime(2007, 10, 1) # 1 October 2007 while True: # skipped some lines irrelevant to the DateTime problem day += 1 try: date = DateTime(self.year, self.month, day) except: break Hm, that should probably be except DateTime.DateTime.DateError but there is not really anything else that can go wrong here. A ConflictError can go wrong here, which is an additional and important reason not to have a bare except. There are good reasons without that, as well. --jcc -- Connexions http://cnx.org Building Websites with Plone http://plonebook.packtpub.com ___ Zope maillist - Zope@zope.org http://mail.zope.org/mailman/listinfo/zope ** No cross posts or HTML encoding! ** (Related lists - http://mail.zope.org/mailman/listinfo/zope-announce http://mail.zope.org/mailman/listinfo/zope-dev )
[Zope] Re: Help with DateTime.earliestTime()
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!
Eric
I'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.
To work around this, I've modified the addition so that instead of adding 1
day, it adds 1.5 days. This extra half a day is removed by the
theDateTime.earliestTime() call but is enough to overcome the DST addition
problem. Ugly hack.
Thanks all.
- Eric
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Re: [Zope] Re: Help with DateTime.earliestTime()
--On 26. August 2007 19:12:18 + 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!
Eric
I'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
pgpOtr6LoOYCd.pgp
Description: PGP signature
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[Zope] Re: Help with DateTime.earliestTime()
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 start2005/10/01 01:00:00 GMT-5 earlyStart=start.earliestTime()
print earlyStart2005/10/01 print earlyStart+312005/11/01
Bad Example: (Here's the problem)
from DateTime import DateTime start=DateTime('2005/10/01 01:00:00
US/Central') print start2005/10/01 01:00:00 US/Central
earlyStart=start.earliestTime
() print earlyStart2005/10/01 print earlyStart+312005/10/31 23:00:00
US/Central
I've confirmed this occurs with several of the US/ timezones (US/Pacific,
US/Alaska, etc)
Can anyone help me figure out why the resulting date is coming up 1 hour
short of the expected 2005/11/01 ?
Thanks!
Eric
[EMAIL PROTECTED] writes:
Sorry for the oversight...This occurs with zope-2.9.5 and zope-2.9.7
Eric
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