Avoided %r formatting on possibly unicode strings.

                # would raise when <mod_path> exists but not <cls_name>, with

                # more context (Python just says "cannot import name ...").

                raise ImportError(

                    "cannot import name %r from %r" % (cls_name, mod_path))

                    "cannot import name '%s' from '%s'" % (cls_name, mod_path))

            # Check for obvious errors. (This check prevents duck typing, but

            # it could be removed if it became a problem in practice.)

            if not issubclass(cls, AppConfig):

                raise ImproperlyConfigured(

                    "%r isn't a subclass of AppConfig." % entry)

                    "'%s' isn't a subclass of AppConfig." % entry)

            # Obtain app name here rather than in AppClass.__init__ to keep

            # all error checking for entries in INSTALLED_APPS in one place.

                app_name = cls.name

            except AttributeError:

                raise ImproperlyConfigured(

                    "%r must supply a name attribute." % entry)

                    "'%s' must supply a name attribute." % entry)

            # Ensure app_names points to a valid module.

            app_module = import_module(app_name)

        app_config = self.app_configs.get(app_label)

        if app_config is None:

            raise LookupError("No installed app with label %r." % app_label)

            raise LookupError("No installed app with label '%s'." % app_label)

        if only_with_models_module and app_config.models_module is None:

            raise LookupError("App with label %r doesn't have a models module." % app_label)

            raise LookupError("App with label '%s' doesn't have a models module." % app_label)

        return app_config

    # This method is performance-critical at least for Django's test suite.