What does '_' do in Django code?

_ is usually a macro/function from gettext, it means the argument is a localized string. this is not limited to Django or Python. in fact gettext is originally a package for C programs, ported to many other languages over the years.

If you look in the import statements, you'll find that they tied _ to a function that turns stuff into unicode and localizes it by writing:

from django.utils.translation import ugettext_lazy as _

_ in Django is a convention that is used for localizing texts. It is an alias for ugettext_lazy. Read Lazy translation in the docs for more info about it.