get_fixed_timezone incorrect with negative timedelta

[Mike Edmunds]

When called with a negative datetime.timedelta, django.utils.timezone.get_fixed_timezone instead creates a timezone with a positive offset 24 hours beyond the negative offset requested:

>>> import datetime
>>> from django.utils.timezone import get_fixed_timezone
>>> get_fixed_timezone(datetime.timedelta(hours=5)).tzname('')
'+0500'  # correct
>>> get_fixed_timezone(datetime.timedelta(hours=-5)).tzname('')
'+1900'  # expected: '-0500'

(tzname is just an easy way to see the problem; it accurately reflects the created timezone's offset.)

This has been broken as far back as I've looked; probably everyone uses get_fixed_timezone with integer minutes rather than a timedelta. Patch follows.

Workaround

If you encounter this in an older version of Django that won't be patched, there's an easy workaround in your code (on Python 2.7 or later). Change:

    tz = get_fixed_timezone(delta)  # where delta is a datetime.timedelta object

to:

    tz = get_fixed_timezone(delta.total_seconds() // 60)

[Mike Edmunds]

PR submitted, suitable for current dev version (and/or as far back as 1.8).

[Tim Graham <timograham@…>]

In d1317ed:

Fixed #28739 -- Fixed get_fixed_timezone() for negative timedeltas.