Gary Poster wrote: > On Sep 6, 2005, at 3:39 PM, Fred Drake wrote:
>> This also brings up a question: How should we deal with timezones for >> historic dates? The specific set of rules that apply to a given date >> or datetime value have to be determined based on both the date and the >> timezone indicator (abbreviation or name), applying the new US rules >> for dates in the past is wrong. Is pytz prepared for this, or do we >> need to figure out how we want to deal with it still? (I do hope all >> the relevant information is in the timezone database, or we'll have to >> think about supporting multiple versions of the database >> simultaneously.) > > I can answer part of this, at least. The Olson database has *very* > detailed about when to apply what time zone, and a cursory glance at it > seems to indicate that the particular new change is right. I also know > pytz works hard to reconcile the very rich Olson data with the datetime > approach (see Stuart's email http://mail.zope.org/pipermail/ > zope3-dev/2005-August/015222.html). > > This may be a bit complicated. I hope Stuart--or Stephan--can shed > some light on the problem. It handles historical and future timezone changes as well as can be done, and I stuffed tests in that demonstrate this (probably where they don't belong, but they are there). There is an issue if timezone definitions change. So for instance, if you pickled a datetime instance for 13:00 1st April 2007 US/Eastern with version 2005k of pytz, if you unpickled it using version 2005m of pytz it would still think it was 13:00 1st April 2007 EST. If you then converted it to UTC and back to US/Eastern (such as done by pytz's normalize() method), you would end up with 14:00 1st April 2007 EDT. This is correct or crap depending on what sort of applications you write :) -- Stuart Bishop <[EMAIL PROTECTED]> http://www.stuartbishop.net/
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