Pass a lazy translation string including variable to function in Django - django

Question

Inside a Django view, I create a subject like that:
subject = _(u"%(user)s has posted a comment") % { 'user': user }
Then I pass this subject to a function, which handles email notifications:
send_notifications(request, subject, url)
In send_notifications, I iterate over all subscriptions and send emails. However, each user can have a different language, so I activate the user's language dynamically via Django's activate:
def send_notifications(request, subject, url):
from django.utils.translation import activate
for s in Subscription.objects.filter(url=url):
activate(s.user.userprofile.lang)
send_mail(subject, render_to_string('notification_email.txt', locals()), settings.SERVER_EMAIL, [s.user.email])
The template gets rendered in the correct language of each user. However, the subject is passed as an evaluated and translated string to send_notifications and thus, is not translated.
I played around with lazy translations and lambda functions as parameters, but without success. Any help appreciated :)

Answer 1

Instead of passing the translated subject, just pass it non translated:
subject = '%(user)s has posted a comment'
context = {'user': user}
def send_notifications(request, subject, url, context):
from django.utils.translation import activate
for s in Subscription.objects.filter(url=url):
activate(s.user.userprofile.lang)
send_mail(_(subject) % context, render_to_string('notification_email.txt', locals()), settings.SERVER_EMAIL, [s.user.email])
If you're not going to personalize the contents per user, then you might as well limit the number of renderings because that's a little confusing:
# also do your imports at the top to catch import issues early
from django.utils.translation import activate
from django.utils.translation import ugettext as _
def send_notifications(request, url,
translatable_subject, context,
body_template='notification_template.txt'):
previous_lang = None
for s in Subscription.objects.filter(url=url).order_by('user__userprofile__lang'):
if s.user.userprofile.lang != previous_lang:
activate(s.user.userprofile.lang)
subject = _(translatable_subject) % context
body = render_to_string(body_template, locals())
send_mail(subject, body, settings.SERVER_EMAIL, [s.user.email])
previous_lang = s.user.userprofile.lang
As such, it is much more obvious that you're not going to render emails per usage.
This slight rewrite should make you doubt about the original choice of a couple of names (locals, notification_template).
The above sample code is barely an "educated guess" and you should double check it and make sure you understand everything before you paste it.

Answer 2

Ok, found a solution myself. In case anybody runs into a similar problem:
from django.utils.translation import ugettext as _
# create subject as raw string in Django view
raw_subject = r"%(username)s has posted a comment"
# for the sake of generic variables, create a dictionary to pass to function
extra_context = { 'user': user }
# call function with raw string and dictionary as params
send_notifications(request, raw_subject, url, extra_context)
# translate the raw string inside send_notifications into the temporarily activated language
translated_subject = _(raw_subject) % extra_context
Appears to be working as desired :) Since we are working with several different notifications, I tried to avoid an extra template for each kind. However, calling a template with extra_context is also a possible solution.

Answer 3

I ended up creating a class that will handle the translation, passing the context of the string to this class.
from django.utils.translation import gettext_lazy as _
class Translatable(object):
def __init__(self, text, context):
self.text = text
self.context = context
def __str__(self):
return _(self.text).format(**self.context)
In your function, just call str(subject):
def send_notifications(request, subject, url):
from django.utils.translation import activate
for s in Subscription.objects.filter(url=url):
activate(s.user.userprofile.lang)
send_mail(str(subject), render_to_string('notification_email.txt', locals()), settings.SERVER_EMAIL, [s.user.email])
And passes subject to your function as following:
subject = Translatable(_("{user} has posted a comment"), context={'user': user})
send_notifications(request, subject, url)