DateTime.DateTime incorrect addition with timezones

[Eric Thomas]

The code snippets below both try to add 31 days to the first day in October 31. I'm expecting this to result in the first day of November (2005/11/1)

Valid behavior:
>>> 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

Invalid behavior: (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 when using the US/ timezones (US/Pacific, US/Alaska, etc)

As you can see, the resulting date is coming up 1 hour short of the expected 2005/11/01.
This problem is known to cause certain products to deadlock a zope instance.

[Colin Watson (cjwatson)]

The datetime project on Launchpad has been archived at the request of the Zope developers (see https://answers.launchpad.net/launchpad/+question/683589 and https://answers.launchpad.net/launchpad/+question/685285). If this bug is still relevant, please refile it at https://github.com/zopefoundation/datetime.