New submission from Yoni Rozenshein <yoni...@gmail.com>:
multiprocessing will attempt to pickle things using ForkingPickler when starting a new process in spawn mode (in Windows this is the only mode, in Linux this is a non-default but settable mode). When run within the context of a unit test, if it has to pickle a TestCase subclass, it encounters objects that can't be pickled. The attached file shows a minimum working example (uncomment the two commented lines under __main__ to run with pytest). When run with unittest.main(), it raises: TypeError: cannot serialize '_io.TextIOWrapper' object When run with pytest.main(), it raises: AttributeError: Can't pickle local object 'ArgumentParser.__init__.<locals>.identity' Note that changing the _child_process in my example to a classmethod/staticmethod or moving it to a top-level function outside the class works around this issue (both with unittest and with pytest). ---------- components: Library (Lib) files: mp_pickle_issues.py messages: 319811 nosy: Yoni Rozenshein priority: normal severity: normal status: open title: [multiprocessing] Multiprocessing in spawn mode doesn't work when the target is a method in a unittest.TestCase subclass, when run either with unittest or with pytest type: behavior versions: Python 3.6, Python 3.7, Python 3.8 Added file: https://bugs.python.org/file47645/mp_pickle_issues.py _______________________________________ Python tracker <rep...@bugs.python.org> <https://bugs.python.org/issue33884> _______________________________________ _______________________________________________ Python-bugs-list mailing list Unsubscribe: https://mail.python.org/mailman/options/python-bugs-list/archive%40mail-archive.com
