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Hi i upgraded to django 1.4 and i want to take advantage of the timezone support, i got a few datetime fields saved in postgres, and they were saved assuming the timezone of my city, once i set

USE_TZ = True

And set the timezone to my city the date filter tags in my templates output the correct hour(timezoned)

{{ concert.datetime|date:'f' }}

The problem is: i use the datetime to build my urls, like this:

{% url event artist_slug=concert.slug_name hour=concert.datetime.hour %}

And those are not correctly timezoned, the hour is still in UTC and that changes my links, something i can't do, it would lose all the page rank and lots of sites link to use, is not feasible, not to mention that it looks weird that the url has a different hour than the one advertised. I tried this:

{% url event artist_slug=concert.slug_name hour=concert.datetime.hour|date:'H' %}

Without success, the date filter tag is not applied and an exception is rised. I have a fairily large codebase and lots of templates, is there any way to fix this without using an accesor that returns the datetime timezoned?

Thank you.

Guillermo Siliceo Trueba
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2 Answers2

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Actually Django Documentation states:

Even if your Web site is available in only one time zone, it’s still good practice to store data in UTC in your database. One main reason is Daylight Saving Time (DST). Many countries have a system of DST, where clocks are moved forward in spring and backward in autumn. If you’re working in local time, you’re likely to encounter errors twice a year, when the transitions happen. (The pytz documentation discusses these issues in greater detail.) This probably doesn’t matter for your blog, but it’s a problem if you over-bill or under-bill your customers by one hour, twice a year, every year. The solution to this problem is to use UTC in the code and use local time only when interacting with end users.

Furthermore:

When time zone support is enabled, Django uses time-zone-aware datetime objects. If your code creates datetime objects, they should be aware too. In this mode, the example above becomes:

import datetime
from django.utils.timezone import utc

now = datetime.datetime.utcnow().replace(tzinfo=utc)

Time zone aware output in templates When you enable time zone support, Django converts aware datetime objects to the current time zone when they’re rendered in templates. This behaves very much like format localization.

And finally, without monkey patching anything: https://docs.djangoproject.com/en/1.6/topics/i18n/timezones/#template-tags

petkostas
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  • Actually i know all these, i have it implemented i got all my internal code using UTC, what i mean is i want all my UTC datetimes automatically localized to the current request tz. It seems such a thing doesnt exists, so i have to change all my code to use an accessor method that does the localization behind the scenes. – Guillermo Siliceo Trueba Jan 18 '14 at 18:52
  • How will you find out the current request TZ (I suppose you are talking about the requesting users TZ)? there is no HTTP method for something like that, additionally why would your project depend on the TZ of the request? If you are not dealing with the user TZ, then as I mentioned above, there are Django ways to manipulate the TZ without needing to monkey patch anything. – petkostas Jan 18 '14 at 22:11
  • I get it through various methods from the user yes, and my application is time sensitive, i don't want to manipulate the TZ i want all the datetimes in the context of that request to be localized to it. – Guillermo Siliceo Trueba Jan 19 '14 at 00:27
  • But the current template is in a timezone context, the timezone of the current user. However, it is only used when the dates are displayed, not any other purposed (such as ifchanged or the usage described above). – Rob Osborne Jan 21 '14 at 21:09
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Unfortunately the only way I found to work with this is to convert the date to users time zone and provide a custom template tag to get the piece you want, something like:

{% url event artist_slug=concert.slug_name hour=concert.datetime|localtime|hour_of_day %}

Where hour_of_day is a custom tag returns the current hour in the correct localtime.

Rob Osborne
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