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Django Tips #18 Difference Between ugettext And ugettext_lazy

Django Tips #18 Difference Between ugettext And ugettext_lazy

The Django translation API provides several utility functions to help you translate your application. They are all available in the django.utils.translation module. For the most cases you will be using ugettext() and ugettext_lazy().

The “u” prefix stands for “unicode”, and usually it is a better idea to use ugettext() instead of gettext(), and ugettext_lazy() instead of gettext_lazy(), since for the most part we will be working with international charsets.

As the name suggests, the “lazy” version of the function holds a reference to the translation string instead of the actual translated text, so the translation occurs when the value is accessed rather than when they’re called.

It’s very important to pay attention to this details, because in a Django project there are several cases where the code is only executed once (on Django startup). That happens with definition modules like models, forms and model forms.

So, what would happen if you use ugettext() (instead of ugettext_lazy()) in a model definition (let’s say on field labels):

  1. Django starts up, the default language is english;
  2. Django picks the english version of the field labels;
  3. The user changes the website language to spanish;
  4. The labels are still displayed in english (because the field definition is called only once; and by the time it was called, the language was other).

To avoid this bahavior, you have to use properly the utility functions.

Here goes a summary of when to use ugettext() or ugettext_lazy():

  • ugettext_lazy():
    • models.py (fields, verbose_name, help_text, methods short_description);
    • forms.py (labels, help_text, empty_label);
    • apps.py (verbose_name).
  • ugettext():
    • views.py
    • Other modules similar to view functions that are executed during the request process