Re: Having trouble understanding Timezone

Ryan

I too went through USE_TZ and time zones etc but too long ago to
remember enough to answer your questions with any authority. However
this works for me ...

USE_TZ = True
TIME_ZONE = 'UTC'

At 18:23 (AESummertime) here in Melbourne Australia I just created a new
record in my Postgres 9.3 database. FWIW the Ubuntu 12.04 database
server runs on local time. I'm using a Windows 8.1 client and Django
1.8.8 dev server.

The model save() method fills in a datetime field if it is blank. It
uses my when() utility. See below.

Examining the new record in the database the date/time saved is ...

2016-01-07 18:23:53.710608+11

There is enough information there to represent a UTC time. Simply
subtract 11 hours. Then add whatever for another timezone. I don't know
if the Django framework does that automatically based on the client
system time but I'm not too concerned about that. I only care that we
are are not losing date/time data.

My when() utility was called by save() without argument. It goes like
this ...

def when(days=0):
"""Function to return a non-naive datetime."""
dday = datetime.now(tz=pytz.utc)
if days == 0:
return dday
ttime = datetime.time(dday)
return timezone.make_aware(datetime.combine(
datetime.fromordinal(dday.toordinal() + days), ttime), pytz.utc)

HTH

Mike


On 7/01/2016 2:36 PM, Ryan Causey wrote:
> Hello,
>
> I'm new to Python and Django so please bear with me on this one.
>
> I've been reading the Django docs, googling, and searching this mailing
> list on the proper configuration and usage of Django when USE_TZ = True.
> However, I'm still a bit fuzzy on things and would like clarification on
> the following:
>
> 1. The documentation says that when USE_TZ = True that "Django stores
> datetime information in UTC in the database, uses time-zone-aware
> datetime objects internally, and translates them to the end user’s
> time zone in templates and forms." Does this mean that the TIME_ZONE
> setting in settings.py should be UTC? Or should it be the timezone
> in which the database server is located?
> 2. I am using a postgresql database, and the installation defaulted the
> database's timezone to my local one. In support of Django storing
> all datetime information in UTC in the database, does the database's
> timezone needs to be set to UTC? Or is it correct for the database's
> timezone to be the local one?
> 3. The documentation also says that one should use the UTC timezone in
> the code, and only convert to local time when dealing with end
> users. I take this to mean that in any code I write I should set
> tzinfo = UTC for all datetime objects I create programmatically and
> let Django translate them in forms and views to the end user's
> timezone automatically. Is this correct?
>
> Thank you in advance for the help,
>
> -Ryan Causey
>
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