ANN: pytz-2004b World timezone library

Tim Peters tim.peters at
Thu Jul 22 03:28:08 CEST 2004

[Stuart Bishop]
> ...
> Note that if you perform date arithmetic on local times that cross DST
> boundaries, the results may be in an incorrect timezone (ie. subtract
> 1 minute from 2002-10-27 1:00 EST and you get 2002-10-27 0:59 EST
> instead of the correct 2002-10-27 1:59 EDT). This cannot be resolved without
> modifying the Python datetime implementation.

That's unlikely to happen.  As designed and documented, datetime
module arithmetic within a single timezone is "naive" arithmetic,
based on Guido's belief that most users most of the time find that
most useful.  The intended way to trip over daylight quirks *when
desired* is to convert to UTC first, do arithmetic in UTC, then
convert back from UTC.

> However, these tzinfo classes provide a normalize() method which allows
> you to correct these values.

That's another idea <wink>.

Thank you for doing this!  I know it's a messy and mostly thankless task.

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