DateTime().strftime('%H:%M') sometimes adds 1 hour

[Nico Grubert]

Suppose we have a list of DateTime() instances like this:

dlist = [DateTime('2008/02/14 14:00:00 GMT+1'), \
         DateTime('2008/02/21 14:00:00 GMT+1'), \
         DateTime('2008/02/28 14:00:00 GMT+1'), \
         DateTime('2008/03/06 14:00:00 GMT+1'), \
         DateTime('2008/03/13 14:00:00 GMT+1'), \
         DateTime('2008/03/20 14:00:00 GMT+1'), \
         DateTime('2008/03/27 14:00:00 GMT+1'), \
         DateTime('2008/04/03 14:00:00 GMT+1'), \
         DateTime('2008/04/10 14:00:00 GMT+1'), \
         DateTime('2008/04/17 14:00:00 GMT+1'), \
         DateTime('2008/04/24 14:00:00 GMT+1'), \
         DateTime('2008/05/01 14:00:00 GMT+1'), \
         DateTime('2008/05/08 14:00:00 GMT+1'), \
         DateTime('2008/05/15 14:00:00 GMT+1'), \
         DateTime('2008/05/22 14:00:00 GMT+1'), \
         DateTime('2008/05/29 14:00:00 GMT+1')]

For some of these instances, the <DateTime() instance>.strftime('%H:%M') returns '15:00' even all instances in this list have '14:00'.

Here is an example (as an External Method for Zope) that demonstrate this DateTime bug:
# -----------------------------------------------------------------------------------------------------------------------------------
from DateTime import DateTime

def test(self):
    """ test
    """
    dlist = [DateTime('2008/02/14 14:00:00 GMT+1'), \
             DateTime('2008/02/21 14:00:00 GMT+1'), \
             DateTime('2008/02/28 14:00:00 GMT+1'), \
             DateTime('2008/03/06 14:00:00 GMT+1'), \
             DateTime('2008/03/13 14:00:00 GMT+1'), \
             DateTime('2008/03/20 14:00:00 GMT+1'), \
             DateTime('2008/03/27 14:00:00 GMT+1'), \
             DateTime('2008/04/03 14:00:00 GMT+1'), \
             DateTime('2008/04/10 14:00:00 GMT+1'), \
             DateTime('2008/04/17 14:00:00 GMT+1'), \
             DateTime('2008/04/24 14:00:00 GMT+1'), \
             DateTime('2008/05/01 14:00:00 GMT+1'), \
             DateTime('2008/05/08 14:00:00 GMT+1'), \
             DateTime('2008/05/15 14:00:00 GMT+1'), \
             DateTime('2008/05/22 14:00:00 GMT+1'), \
             DateTime('2008/05/29 14:00:00 GMT+1')]

    hm = '14:00'
    for d in dlist:
        if d.strftime('%H:%M') != '14:00':
            # -> ['DateError?', DateTime('2008/04/03 14:00:00 GMT+1'), '15:00']
            return ['DateError?', d, d.strftime('%H:%M')]
# -----------------------------------------------------------------------------------------------------------------------------------

[Nico Grubert (nicogrubert-gmail)]

This happens in Zope 2.9.6, 2.9.7, 2.9.8.
In Zope 2.10 everything works fine.

[Andreas Jung (ajung)]

This is a daylight saving issue. Since you specify the timezone, the daylight saving is taken into account when calling strtfime().