On Mon, Dec 1, 2014 at 12:59 AM, Nathaniel Smith <n...@pobox.com> wrote: > On Sun, Nov 30, 2014 at 10:14 PM, Mark Shannon <m...@hotpy.org> wrote: >> Hi, >> >> This discussion has been going on for a while, but no one has questioned the >> basic premise. Does this needs any change to the language or interpreter? >> >> I believe it does not. I'm modified your original metamodule.py to not use >> ctypes and support reloading: >> https://gist.github.com/markshannon/1868e7e6115d70ce6e76 > > Interesting approach! > > As written, your code will blow up on any python < 3.4, because when > old_module gets deallocated it'll wipe the module dict clean. And I > guess even on >=3.4, this might still happen if old_module somehow > manages to get itself into a reference loop before getting > deallocated. (Hopefully not, but what a nightmare to debug if it did.) > However, both of these issues can be fixed by stashing a reference to > old_module somewhere in new_module. > > The __class__ = ModuleType trick is super-clever but makes me > irrationally uncomfortable. I know that this is documented as a valid > method of fooling isinstance(), but I didn't know that until your > yesterday, and the idea of objects where type(foo) is not > foo.__class__ strikes me as somewhat blasphemous. Maybe this is all > fine though. > > The pseudo-module objects generated this way will still won't pass > PyModule_Check, so in theory this could produce behavioural > differences. I can't name any specific places where this will break > things, though. From a quick skim of the CPython source, a few > observations: It means the PyModule_* API functions won't work (e.g. > PyModule_GetDict); maybe these aren't used enough to matter. It looks > like the __reduce__ methods on "method objects" > (Objects/methodobject.c) have a special check for ->m_self being a > module object, and won't pickle correctly if ->m_self ends up pointing > to one of these pseudo-modules. I have no idea how one ends up with a > method whose ->m_self points to a module object, though -- maybe it > never actually happens. PyImport_Cleanup treats module objects > differently from non-module objects during shutdown.
Actually, there is one showstopper here -- in the first version where reload() uses isinstance() is actually 3.4. Before that you need a real module subtype for reload to work. But this is in principle workaroundable by using subclassing + ctypes on old versions of python and the __class__ = hack on new versions. > I guess it also has the mild limitation that it doesn't work with > extension modules, but eh. Mostly I'd be nervous about the two points > above. > > -n > > -- > Nathaniel J. Smith > Postdoctoral researcher - Informatics - University of Edinburgh > http://vorpus.org -- Nathaniel J. Smith Postdoctoral researcher - Informatics - University of Edinburgh http://vorpus.org _______________________________________________ Python-Dev mailing list Python-Dev@python.org https://mail.python.org/mailman/listinfo/python-dev Unsubscribe: https://mail.python.org/mailman/options/python-dev/archive%40mail-archive.com
