diff --git a/docs/internals/contributing.txt b/docs/internals/contributing.txt index 1f1161de43..1ad794230e 100644 --- a/docs/internals/contributing.txt +++ b/docs/internals/contributing.txt @@ -426,6 +426,47 @@ translated, here's what to do: .. _Django i18n mailing list: http://groups.google.com/group/django-i18n/ +Django conventions +================== + +Various Django-specific code issues are detailed in this section. + +Use of ``django.conf.settings`` +------------------------------- + +Modules should not in general use settings stored in ``django.conf.settings`` at +the top level (i.e. evaluated when the module is imported). The explanation for +this is as follows: + +Manual configuration of settings (i.e. not relying on the +``DJANGO_SETTINGS_MODULE`` environment variable) is allowed and possible as +follows:: + + from django.conf import settings + + settings.configure({}, SOME_SETTING='foo') + +However, if any setting is accessed before the ``settings.configure`` line, this +will not work. (Internally, ``setttings`` is a ``LazyObject`` which configures +itself automatically when the settings are accessed if it has not already been +configured). + +So, if there is a module containg some code as follows:: + + from django.conf import settings + from django.core.urlresolvers import get_callable + + default_foo_view = get_callable(settings.FOO_VIEW) + +...then importing this module will cause the settings object to be configured. +That means that the ability for third parties to import the module at the top +level is incompatible with the ability to configure the settings object +manually, or makes it very difficult in some circumstances. + +Instead of the above code, a level of laziness or indirection must be used, such +as :class:`django.utils.functional.LazyObject`, :func:`django.utils.functional.lazy` or +``lambda``. + Coding style ============