celery: introduce make_app instead of creating app at import time It is dirty to instantiate things at import time (unless it really is basic singletons). In 0.5.1 (and earlier), such dirtyness made partial test execution fail when other things had global side effects and things didn't use the usual import order: $ py.test kallithea/lib/ collecting ... ――― kallithea/lib/celerypylons/__init__.py ――― kallithea/lib/celerypylons/__init__.py:58: in <module> app.config_from_object(celery_config(tg.config)) kallithea/lib/celerypylons/__init__.py:28: in celery_config assert config['celery.imports'] == 'kallithea.lib.celerylib.tasks', 'Kallithea Celery configuration has not been loaded' data/env/lib/python2.7/site-packages/tg/configuration/tgconfig.py:31: in __getitem__ return self.config_proxy.current_conf()[key] E KeyError: 'celery.imports' Avoid that by running a "factory" function when the celery app actually is needed.