django 1.4 - can't compare offset-naive and offset-aware datetimes

Question

I am in the process of migrating an application from django 1.2 To 1.4.

I have a daily task object which contains a time of day that task should be completed:

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Answer 1

Check the thorough document for detail info.

Normally, use django.utils.timezone.now to make an offset-aware current datetime

>>> from django.utils import timezone
>>> timezone.now()
datetime.datetime(2012, 5, 18, 13, 0, 49, 803031, tzinfo=<UTC>)

And django.utils.timezone.make_aware to make an offset-aware datetime

>>> timezone.make_aware(datetime.datetime.now(), timezone.get_default_timezone())
datetime.datetime(2012, 5, 18, 21, 5, 53, 266396, tzinfo=<DstTzInfo 'Asia/Shanghai' CST+8:00:00 STD>)

You could then compare both offset-aware datetimes w/o trouble.

Furthermore, you could convert offset-awared datetime to offset-naive datetime by stripping off timezone info, then it could be compared w/ normal datetime.datetime.now(), under utc.

>>> t = timezone.now() # offset-awared datetime
>>> t.astimezone(timezone.utc).replace(tzinfo=None)
datetime.datetime(2012, 5, 18, 13, 11, 30, 705324)

USE_TZ is True 'by default' (actually it's False by default, but the settings.py file generated by django-admin.py startproject set it to True), then if your DB supports timezone-aware times, values of time-related model fields would be timezone-aware. you could disable it by setting USE_TZ=False(or simply remove USE_TZ=True) in settings.