ugettext and ugettext_lazy functions not recognized by makemessages in Python Django

Question

I'm working with Django 1.5.1 and I'm experiencing some "strange behaviour" with translations. I'm using ugettext and ugettext_lazy in the same Python file. If I organize the imports as:

from django.utils.translation import ugettext as trans
from django.utils.translation import ugettext_lazy as _

or

from django.utils.translation import ugettext as trans, ugettext_lazy as _

The strings marked as trans("string") are skipped when running makemessages command.

However, if I don't rename the ugettext it works well with both versions:

from django.utils.translation import ugettext
from django.utils.translation import ugettext_lazy as _

or

from django.utils.translation import ugettext, ugettext_lazy as _

Now trans("string") works well.

So, does anybody know why this import renaming is causing the renamed function not to be called? Is this an actual Python "limitation" I didn't know when renaming more than one function inside the same module?

---

UPDATE

After some testing, I've realized that even creating an empty python module inside an app with the following code it doesn't work:

from django.utils.translation import ugettext_lazy as translate

a = translate("string")

However, if using _ for the alias it works:

from django.utils.translation import ugettext_lazy as _

a = _("string")

My conclusion is: You can only use the _ alias for ugettext and ugettext_lazy (or any other related translation function) in Django or else it won't be recognized by makemessages command. The technical explanation can be found in Robert Lujo's answer.

Thanks!

Answer 1

Django command utility makemessages internally calls xgettext program like this:

cmd = (
    'xgettext -d %s -L Python %s %s --keyword=gettext_noop '
    '--keyword=gettext_lazy --keyword=ngettext_lazy:1,2 '
    '--keyword=ugettext_noop --keyword=ugettext_lazy '
    '--keyword=ungettext_lazy:1,2 --keyword=pgettext:1c,2 '
    '--keyword=npgettext:1c,2,3 --keyword=pgettext_lazy:1c,2 '
    '--keyword=npgettext_lazy:1c,2,3 --from-code UTF-8 '
    '--add-comments=Translators -o - "%s"' %
    (domain, wrap, location, work_file))

(source can be found here). So, some keywords are predefined by the xgettext utility (check reference for --keyword):

• for python - gettext, ugettext, dgettext, ngettext, ungettext, dngettext, _

and some are added by django utility:

• gettext_lazy , ngettext_lazy , ugettext_noop , ugettext_lazy , ungettext_lazy , pgettext , npgettext , pgettext_lazy , npgettext_lazy

Keyword trans is not in any of these keyword sets, so you should not use it for marking texts for translations.