New submission from Michael Foord <mich...@voidspace.org.uk>: Pickling uses __class__ instead of type(obj) to determine the type to pickle. This means that objects which pretend to be other objects (like proxy and mock objects) can't be pickled correctly:
>>> class Foo(object): ... __class__ = property(lambda *a, **k: int) ... ... >>> from pickle import dumps >>> dumps(Foo()) b'\x80\x03cbuiltins\nint\nq\x00)\x81q\x01}q\x02b.' Here Foo() is pickled as an int. In Python 2 using type(obj) wouldn't work for old style classes, but I don't see a reason not to use type(obj) in Python 3. Note that also, the pickle protocol methods like __getstate__ etc are looked up on the object instance (using getattr) rather than on the object type. This means that __getattr__ is invoked to look them up - requiring special casing in objects that provide __getattr__ to avoid them (raise an AttributeError if they don't provide these methods). This affects three object types in the unittest.mock namespace (_Call, sentinel and the Mock variants). ---------- messages: 158254 nosy: michael.foord priority: normal severity: normal status: open title: pickling uses __class__ so you can't pickle proxy/mock objects that pretend to be other objects _______________________________________ Python tracker <rep...@bugs.python.org> <http://bugs.python.org/issue14577> _______________________________________ _______________________________________________ Python-bugs-list mailing list Unsubscribe: http://mail.python.org/mailman/options/python-bugs-list/archive%40mail-archive.com
