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Django tips and tricks

How to make django timezone aware on Django tips and tricks

Feb. 23, 2018, 2:34 a.m.

As far as I know there is no way for the browser to tell the application what is the user's timezone.
That is a problem when you want to run an international site, mostly when users from different places save time related stuff.
Some people suggest to just ask the user what his timezone is.
I did not want to bother them with that, so I created this little hack.
this involves a context processor and some javascript.

So lets start with the context processor in django.
you start by writing your context_processor.py file

 from django.utils import timezone
 def timezone_processor(request):
     # look for a cookie that we expect to have the timezone
     tz = request.COOKIES.get('local_timezone', None)
     if tz:
         tz_int = int(tz) # cast to int
         # here we decide what will prefix timezone number
         # the output of tz_str will be something like: 
         #                Etc/GMT+1, GMT+0, Etc/GMT-2
         if tz_int >= 0:
             tz_str = 'Etc/GMT+'+tz
         else:
             tz_str = 'Etc/GMT'+tz
         # this forces timezone
         timezone.activate(tz_str)
     # Now we tell the template that we have a timezone
     return {'local_timezone': tz}

For the context processor to work you must declare it in settings.py

 TEMPLATES = [
     {
         .........
         'OPTIONS': {
             'context_processors': [
                 .........
                 'myapp.context_processors.timezone_processor',
             ],
         },

Ok, so this code just create a timezone string and activates it.
A template context processor returns a dictionary that will be sent to the context of the template when rendering. Here we are returning local_timezone.
But where this cookie come from? Lets go to the template and make this javascript trick.

 <!-- if django already knows timezone we will not run it again -->
 {% if not local_timezone %}
     <!-- getTimezoneOffset does the trick! -->
     <!-- it return minutes so we divide to get hours -->
     timezone = new Date().getTimezoneOffset() / 60;
     document.cookie = 'local_timezone=" + timezone;
     <!-- set a cookie with this value and we are done -->
 {% endif %}