[Zope-dev] DateTime issues with negative offsets

[Juan A. Diaz]

Hi all,

I found a issue with the DateTime module. For what I could see the
functions _tzoffset2rfc822zone and _tzoffset2iso8601zone, that are
used to return a zone specification, have problems with negative
offset. This not happens with all the negative offset, just when the
hour is not rounded and have minutes.

Functions '_tzoffset2rfc822zone' and '_tzoffset2iso8601zonethat' are
used in the mtehods 'DateTime.ISO8601' and 'DateTime.rfc822'.

I think it may be clearer with some examples:

>>>  dt = DateTime('2004/06/14 14:30:15 GMT+0430')
>>>  dt.rfc822()
'Mon, 14 Jun 2004 14:30:15 +0430'
>>>  dt.ISO8601()
'2004-06-14T14:30:15+04:30'

This is Ok.

>>>  dt = DateTime('2004/06/14 14:30:15 GMT-0400')
>>>  dt.rfc822()
'Mon, 14 Jun 2004 14:30:15 -0400'
>>>  dt.ISO8601()
'2004-06-14T14:30:15-04:00'

This is Ok.

>>>  dt = DateTime('2004/06/14 14:30:15 GMT-0430')
>>>  dt.rfc822()
'Mon, 14 Jun 2004 14:30:15 -0530'
>>>  dt.ISO8601()
'2004-06-14T14:30:15-05:30'

This is not. As you could see, the offset printed is -0530.

This is the code for both functions

def _tzoffset2rfc822zone(seconds):
    """Takes an offset, such as from _tzoffset(), and returns an
rfc822
       compliant zone specification. Please note that the result of
       _tzoffset() is the negative of what time.localzone and time.altzone is.
    """
    return "%+03d%02d" % divmod((seconds / 60), 60)


def _tzoffset2iso8601zone(seconds):
    """Takes an offset, such as from _tzoffset(), and returns an ISO 8601
       compliant zone specification. Please note that the result of
       _tzoffset() is the negative of what time.localzone and time.altzone is.
    """
    return "%+03d:%02d" % divmod((seconds / 60), 60)

I think that the error come from the way in where the integer division works.


>>> secconds = (4 * 60 + 30) * 60
>>> secconds
16200
>>> divmod((secconds/60), 60)
(4, 30)
>>> divmod((-secconds/60), 60)
(-5, 30)


>>> secconds / 60
270
>>> 270 / 60
4
>>> - 270 / 60
-5
>>>

I hope be clear and not to much verbose, but this is my first mail to the list.
Cheers and sorry for my English :)

nueces....