When patching a class, mock.create_autospec() correctly detects properties and __slot__ attributes, but not subclasses of property() or other kinds of data descriptors. The attached patch detects all data descriptors and patch them the way they should be.

Updated patch with review comments.

New changeset e947248100ae by Gregory P. Smith in branch '3.5': Issue #26750: unittest.mock.create_autospec() now works properly https://hg.python.org/cpython/rev/e947248100ae New changeset 0bc14c91ef7e by Gregory P. Smith in branch 'default': Issue #26750: unittest.mock.create_autospec() now works properly for https://hg.python.org/cpython/rev/0bc14c91ef7e

Thanks! Is there a reason not to use inspect.isdatadescriptor() instead of _is_data_descriptor()?

Probably just Amaury and I forgetting that existed. Amaury, inspect.isdatadescriptor's implementation is a bit different than this change's _is_data_descriptor. Thoughts?

New changeset 3ff02380b1bf by Gregory P. Smith in branch '3.5': Issue #26750: use inspect.isdatadescriptor instead of our own https://hg.python.org/cpython/rev/3ff02380b1bf New changeset d51a66622266 by Gregory P. Smith in branch 'default': Issue #26750: use inspect.isdatadescriptor instead of our own https://hg.python.org/cpython/rev/d51a66622266

inspect.isdatadescriptor() is better indeed. (I was initially working on an old version of mock.py which does not import inspect, and I did not want to add the dependency there). - inspect uses hasattr(type(obj)) instead of hasatr(obj). This is better, (but does not work for 2.x old-style classes) - my patch tested for __del__... this is completely wrong, it should have been __delete__. oops. inspect.isdatadescriptor() does not test for __delete__. This is insaccurate, but I doubt it will ever matter. This is only possible for Python-defined descriptors, the C implementation always exposes both __set__ and __delete__ when tp_set is filled. IOW, I'm happy with the current state.