'date' template filter displays certain timezones incorrectly

[Drew Roos]

the date template filter will display the wrong timezone offset, if that timezone is a partial-hour offset from UTC, and is west of UTC (negative offset).

>> from django.utils.dateformat import format
>> import pytz
>> from datetime import datetime

>> x = pytz.UTC.localize(datetime(2011, 1, 1)).astimezone(pytz.timezone('America/St_Johns'))
>> format(x, 'O')
u'-0430'

>> y = pytz.UTC.localize(datetime(1970, 1, 1)).astimezone(pytz.timezone('Africa/Monrovia'))
>> format(y, 'O')
u'-0116'

the correct offsets are -0330 and -0044, respectively.

[Aymeric Augustin]

Indeed, the arithmetic at https://code.djangoproject.com/browser/django/trunk/django/utils/dateformat.py#L184
is incorrect for negative values:

>>> seconds = 600
>>> u"%+03d%02d" % (seconds // 3600, (seconds // 60) % 60)
u'+0010'
>>> seconds = -600
>>> u"%+03d%02d" % (seconds // 3600, (seconds // 60) % 60)
u'-0150'

[Drew Roos]

patch to fix bug

[Aymeric Augustin]

math.copysign makes the code a bit hard to read.

Wouldn't this be more explicit?

sign = '-' if seconds < 0 else '+'
seconds = abs(seconds)
return '%s%02d%02d" % (sign, seconds // 3600, (seconds // 60) % 60)

This will need a regression test, too.

[Ramiro Morales]

In [16903]:

Fixed #16924 -- Corrected date template filter handling of negative (West of UTC) timezone offsets.

The 'O' format specifier output was incorrect. Thanks mrgriscom and Aymeric Augustin.