django timezone view handling

One simple way to handle user-time-zone localization in an app is to always store the timestamp in UTC, and localize viewing/editing of that timestamp in a specific timezone.

By default, Django traffics in the single settings.py-configured timezone.

Timezone handling appear incomplete. The two options you'll run across are this snippet for a timezone-localizing filter and django-timezones.

django-timezones has support for a TimeZone model/view field, and a model/view LocalizedDateTimeField. The View field, however, will only do the parse-time conversion of the datetime value in to the settings-defined TZ. This only solves half of the problem, since you still need to convert the settings-defined TZ into the user's TZ, and there's no component for that.

The following is a LocalizedDateTimeInput widget which will handle this last step, building on django.forms.DateTimeInput and django-timezones' utility code:

from django import forms
from timezones.utils import adjust_datetime_to_timezone

class LocalizedDateTimeInput (forms.DateTimeInput):
    def __init__(self, tz):
        self._tz = tz
        super(LocalizedDateTimeInput, self).__init__()

    def render(self, name, value, attrs=None):
        if isinstance(value, datetime):
            value = adjust_datetime_to_timezone(value, 'UTC', self._tz)
        # @fixme: output the string rep of the timezone, probably after the <input />
        return super(LocalizedDateTimeInput, self).render(name, value, attrs)

Unfortunately, you'll need to add a level of indirection to your view Form constructors to bind the 'tz' argument on the widget. Instead of a normal:

class MumbleForm (forms.Form):
    name = forms.CharField()
    date = forms.DateTimeField()

You'll want to do something like:

def MumbleForm(user, *args, **kwargs):
    tz = settings.TIME_ZONE
    if user and hasattr(user, 'get_profile'):
        tz = user.get_profile().timezone

    class _MumbleForm (forms.Form):
        name = forms.CharField()
        date = LocalizedDateTimeField(tz, widget=LocalizedDateTimeInput(tz))

    return _MumbleForm(*args, **kwargs)

You can see more usage examples from the brew-journal commit.

Any tips or improvements welcome, of course.

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